spekkio, hard to say with metroid if the color shader is correct. I would need to fire up mGBA myself with F-Zero MV to tell you for sure how authentic the colors are (the backgrounds on the queen cup tenth zone east track, or the 3rd stark farm circuit background from the second cup are distintively too bright in emulators, on the ds lite or the on a gamecube gameboy player via GBi played on a CRT, even with the GBA color matrix in the last case) or advance wars (grass shade of plain tiles is more green/natural than the bright yellowish VBA for instance shows).
If you ask me it might be a bit too de-saturated.
The LCD grid is fine and actually you should check how it looks with just it enabled, as it should darken the image a bit.
Also bear in mind that while the OG GBA did look that dark and some games (F-Zero: Maximum Velocity and Advance Wars definitely) were designed with that screen in mind and thus looked oversaturated/garish on a PC monitor or more modern handheld, while some fucked it up by not caring how dark the art looks on the actual GBA screen since the bulk of the dev work was done on PCs with CRTs anyway (castlevania: circle of the moon, which got criticized in reviews for being fucking dark, also the official port of Doom) or aimed for the GBA SP's lit screen (the SP was announced very fast). Thus the "no color shader" look with an LCD grid to me would absolutely fine apart from a few cases of earlier titles where developers cared about it.
Metroid Fusion, Warioland IV and Castlevania Aria of Sorrow are three cases where I honestly don't know if they were aiming for the SP's lit screen or not. Things got muddy later on since some people had OG GBAs and some SPs (and a few GB Players), few games had a brightness setting/mode.
Having said all of that I prefer my DS lite's screen (I think I have the IPS one, apparently they made some with those, but it's a lottery) for pretty much everything apart from F-Zero Maximum Velocity, those track backgrounds just look wrong there.