Color How can I darken the color output?

It sounds like you have the unit's analog video outputs connected to a TV/Video combo or some time of a recording device. Going through a recording device can cause the image to brighten and darken.

You can usually can only alter or darken a print colour from the software program (i.e. Word), then send your document to the printer.

Each filter intensifies its color and darkens others, especially the color opposite on the color wheel. They're not of much use in color photography, unless you want weird color casts, but they come into their own in black&white photography.
For example, a red filter intensifies red and darkens blue. It can make a sky look almost black, making clouds pop out. Similarly it can darken foliage. A green filter on the other hand will brighten foliage.
If your camera can take black&white photos, try taking pictures of a red rose with green leaves with and without the filters. With one combination the rose and the leaves will be the same shade. With a red filter the rose will be bright against the dark leaves. With a green filter you'll get a dark rose with bright leaves.
With digital photography you can achieve the same effect in postprocessing, but some times its easier to get the result in camera.

It is very common for the color of the lamp to change as it nears the end of it's life. Depending on the bulb itself you may see yellow, green, or blue shifts (I have even seen red/orange). This is due to the diminishing output of the bulb and while you can make some adjustment you will eventually hit the point of failure. The bulb could in fact last several more weeks or even months depending on your use and environment. It is probably a good time to start searching for a replacement now so you can replace it as soon as it dies or just replace it now if the color is too bad to be worthwhile.

you probably need to clean lens and optics in the light engine.Also if it is a lcd projector inside of the light engine in front of the lcd is a glass color filter one for red ,green,blue they can darken and lose or even change color.I would clean optics and check and clean filters.Or you could replace light engine.

CHECK TO SEE IF YOU HAV THE TEX ON IN THE MEAU IF SO TURN IT OFF

you may have just put it into fade out. find thee fade out control and reverse it the mode. hope that works.
DFD

i would suggest that 1st you do the auto gradation adjustment full adjust under add function /adjustment cleaning then under additional functions look for one that says printer settings you can adjust black density under that setting

First clean the cartridge and then go to toolbox and give test print.

Have you tried doing a recalibration cycle ? Had trouble here following installing a new blue toner. Everything was TOO intense. Tried turning power on and off a few times and then finally found the route to forcing a full re-calibration.  Ready -->Menu select -->Menu Engine --> >Engine service -->Color calibration. 
Now if we could just get rid of these lousy streaks on the side  =<