no photos of screen posted, makes this hard to guess.
carbon dated at 2002 , its 15 years old and the CCFL is not burned out, now that is amazing ! but I bet the CCFL is dim and yellow.
so when that happens all colors are no yellow added.
ok you proved the display is bad. or set wrong (NICE JOB)
did you push the screens menu key and see all those settings inside.?
on the last screen of most hp, OSD
screens is a reset.
did you try that, reset to factory setting. do you have the users guide.
or buy a new screen at walmart for $50? (a fraction of cost to fix yours, for sure)
that monitor is old a COMPAQ in fact
1024 x 768 (limited here, and very very poor that)
HP has minimal support , mostly none on this old mon.
https://support.hp.com/us-en/document/c00343350#AbT0
the screen is worth $20 working or $5 not.
so why not buy $60 new one.
and the age of high resolution ! then get rid of XP, its a virus magnet.
id do this, id go here and get a far better monitor with LED back lamps that do not go dim or turn yellow.
even free shipping now.
https://www.walmart.com/search/?cat_id=0&page=1&query=computer+monitor&sort=price_low#searchProductResult
now the fiddling answers, just a few. im reading your manual to you.
ok./ page 14
first is OSD
try the 2 cooler temperatures yet>?
or page 15 the factor RESET?
or the autoadjust button?
https://www.manualslib.com/manual/680956/Compaq-Tft5010.html?page=14#manual