Color transparencies are dark & poor color

Plain paper (60 to 90 g/m2), heavy paper (91 to 163 g/m2), envelope
(Envelope DL, Envelope COM10, Envelope C5, Envelope
Monarch, Envelope B5), label sheet, transparency ((Black and white
printing only)

Here is the manual for your printer with instructions:
http://www.lexmark.com/publications/eng/7100/index.html
Here is the full spec info on your printer.
Print Resolution:
4800x1200 dpi best mode - Photo paper
2400x1200 dpi best mode - All other media
Print Speed:
mono draft mode 22 ppm
color draft mode 15 ppm
Copy Speed:
mono draft mode 22 ppm
color draft mode 14 ppm
Fax Speed:
33.6 Kbps
Cartridge Compatibility:

• Black: Moderate Yield – 32
• Black: Standard Yield – 34
• Color: Moderate Yield – 33
• Color: Standard Yield – 35
• Photo: Standard Yield – 31

Connectivity:
USB only
Media Handling:
Paper: Up to 150 sheets (20 lb or 75 g/m2 bond)

• Envelopes: 15 envelopes
• Labels: 35 sheets
• Transparencies: 75 transparencies
• Hagaki: 45 cards
• Card stock: 35 sheets

Size & Weight:
490.8mm x 422.7mm x 305.4mm (W x D x H)
9.34kg
Scan Resolution:

• Optical: 1200ppi
• Interpolated: 19,200 x 19,200

Print and screen color matching is HORRIBLY difficult. It could be a case of old ink, humid air, poor calibration, or different qualities of paper (when comparing two prints).

For best, most consistent products, go to a professional photo finisher/print shop.

Shaking these cartridges does nothing except give you a little exercise. If this is a brand new HP cartridge you are having problems with I would return it to the store you purchased it from. HP brand cartridges should not give you these problems right out of the box. The print defects you are seeing are due to a dried up or clogged print head. If you like you can try hydrating the print head on a water soaked paper towel until the ink starts flowing, but there's a risk you will cross contaminate the colors.

Hi manitou344:
Here is some info that might help you.

Table 1-8. Tray 1 paper sizes1
Media Dimensions Weight or thickness Capacity
Minimum size paper 76 by 127 mm
(3 by 5 in)
60 to 163 g/m2
(16 to 43 lb bond)
100 sheets
(75 g/m2; 20 lb bond)
Maximum size paper 216 by 356 mm
(8.5 by 14 in)
60 to 163 g/m2
(16 to 43 lb bond)
100 sheets
(75 g/m2; 20 lb bond)
Minimum size glossy
paper
76 by 127 mm
(3 by 5 in)
75 to 120 g/m2
(20 to 32 lb bond)
Maximum stack
height: 12 mm (0.47 in)
Maximum size glossy
paper
216 by 356 mm
(8.5 by 14 in)
75 to 120 g/m2
(20 to 32 lb bond)
Maximum stack
height: 12 mm (0.47 in)
Minimum size
transparencies2
76 by 127 mm
(3 by 5 in)
0.12 to 0.13 mm thick
(4.7 to 5 mils thick)
50 sheets
Maximum size
transparencies2
216 by 356 mm
(8.5 by 14 in)
0.12 to 0.13 mm thick
(4.7 to 5 mils thick)
50 sheets
Minimum size
envelopes
76 by 127 mm
(3 by 5 in)
60 to 90 g/m2
(16 to 24 lb bond)
10 sheets
Maximum size
envelopes
216 by 356 mm
(8.5 by 14 in)
60 to 90 g/m2
(16 to 24 lb bond)
10 sheets
Minimum size label 76 by 127 mm
(3 by 5 in)
75 to 163 g/m2
(20 to 43 lb bond)
50 sheets
Maximum size label 216 by 356 mm
(8.5 by 14 in)
75 to 163 g/m2
(20 to 43 lb bond)
50 sheets
Minimum size
cardstock
76 by 127 mm
(3 by 5 in)
135 to 216 g/m2
(43 to 43 lb bond)
50 sheets
Maximum size
cardstock
216 by 356 mm
(8.5 by 14 in)
135 to 216 g/m2
(43 to 43 lb bond)
50 sheets
This printer can
detect transparencies that were not designed for use with HP Color LaserJet printers.

Did you just replace the toners? are you using generic? I have seen some colors off due to generic toners, (could be a bad batch).
Also, there should a be screen in the Menu section where you can try adjusting the color or
Re-calibrate it ( I would try this 1st)
Print out a Demo sheet it will give you a color test sheet how does it look?
I am not a color copier specialist but have worked w/techs that are, but i work on color printers, ususally same principle.
Also look for a screen called Configuration page this will tell you the settings of the copier and may actually tell you if a color is off.
the problem is you have to have a service manual because you are dealing with adjustments on an X-Y plane.

That stock might be too heavy for a bizhub.

Specifications state the following:

Plain paper (16 lb to 24 lb),
thick paper 1 (24-1/4 lb to 40 lb),
thick paper 2 (40-1/4lb to 55-1/2 lb),
thick paper 3 (55-3/4 lb to 68 lb),
thick paper 4 (68-1/4 lb to 72 lb)*, OHP transparencies*, postcards*, letterheads,
colored paper, envelopes*, label sheets*, banner paper (24-1/4 lb to 55-1/2 lb)*
Duplex: Plain paper (17 lb to 24 lb), thick paper1/2/3 (24 lb to 68 lb
*Can only be fed through the bypass tray.

These specs are directly from the user guide.

Is the paper running through the bypass tray?

Since you are doing transparencies just make sure it is for HP also there may be a weight problem. You see as the sheet goes though it can cause a buckle to which now the print cartridge is not touching any longer.

Looks like you need some printer profiling...
Washed out prints can be caused by several things... Let's see if we can sort it out.
It could be your printer, or it could be your monitor giving you false readings.
Printer Profiles: If you do not have the correct printer profile, then your prints may turn out faded. This is a gamma thing. You are encouraged to calibrate your monitor, and go to the printer manufacturer web site and look up your printer to see if they offer the correct RGB and CYMK printer profile.
Poor quality paper: most likely the problem is a poor quality paper. You did not indicate what printer and what paper you are using, so we cannot help much. However, try a sheet of the high quality photo paper and see if the colors print more vivid and saturated.
If the above doesn't help, I suggest you find someone else with a different printer who is willing to bring it over and print from your computer. That will proof the printer either in or out of the equation.
If none of this helps let us know and we'll walk you through the creation of a custom printer profile and custom color space.

hello,
probably the printer takes his own color-profiles installed by epson.
Click on propriaties of the printer and create your own color-profile for diferent sizes.
you can take the color-profile from a smaler size and save it choosing an other size.
So You also can improove your pictures by changing the color-profile after your needs...
but then you should use the same paper , because different papers give different colors.
you can also improove the colors by choosing-on the profile-another type of paper.

i hope i could help