There is another possibility, too. Even more common than OEM screens, are OEM digitizers. N900's digitizer have characteristic, that should help our trans-reflective screen to work properly in direct sun - namely, it's so-called "sunglasses effect",when you look on the digitizer alone.

There is a slight possibility, that your LCD is genuine, but digitizer is replacement, with different tint, that makes colours offset. You could check it by disassembling screen, connecting every tape *without* putting screen back together, and checking, if sole LCD is indeed giving tinted colours (as you've noticed, it's most visible for whites).

Now, I wouldn't put my money on it - I suspect that both screen and digitizer is OEM - but, comparing both components to original ones, you may pinpoint which element is responsible. If it's the LCD indeed, you're in even more luck, IMO - there are tons of non-working N900's (broken ports + requiring reflash, broken modem, or broken everything) with vandalized digitizers, but LCDs intact. If the colours bothers you, you could get one of those, and replace screen.

To be honest, it's much harder to find genuine digitizer in mint condition (and N900's resistive touch is of fantastic quality, which many times isn't reproduced appropriately in OEMs), than mint LCD.

To be honest, I had accident with N900 during summer (it fell from 5 cm height, but hit ceramic edge of cup - result, broken LCD. for comparison, some time before it felt from more than 2 meters into terracotta floor - but without hitting any edges - and wasn't even scratched, modded mugen backcover absorbed whole impact, shredding to pieces in the process) and I was glad that it was broken LCD, not broken digitizer. Replaced it with one of my surplus LCDs, without any problems.

/Estel