I've noticed the color issue and progressive scan issues as well. Ps2_emu actually switches to 480p output signal and doesn't look too great. This left me scratching my head wondering wtf was going on. Turns out it's not a bug, but a regular feature, ha.
Another advantage ps2_gxemu has, it increases the vertical resolution that the games are rendered at internally. This is noticeable in one of my all time favorite games, Capcom vs SNK 2 which has 2d sprites in front of 3d stages. This game is normally rendered at 640x224 with an interlaced output. Great on a CRT, not so much on a modern 4k TV.
Running CvS2 on ps2_emu, the backgrounds have a highly noticeable stairstep/Lego effect on the edges. This jagged effect is noticeable on ps2_netemu as well. The smoothing options help a bit but not enough imo. An unfortunate side effect of de-interlacing the output but not increasing vertical resolution.
The edges are cleaned up quite a bit on ps2_gxemu thanks to the increase of vertical render resolution. The smoothing filter is great also and further improves edge quality. I have to patch the game itself to render internally at 640x448 so that ps2_emu looks closer to ps2_gxemu.
I did test ps2_netemu with the patches I mentioned, unfortunately the frame rate drops below 60fps substantially and is unacceptable, specifically for a fighting game. It's a damn shame because the game looks great, and the ps2_netemu smoothing filter does an excellent job of cleaning up the 2d sprites thus making them look more modern and suitable for High-def displays.
Oh, did mention patches? Ha, I learned that ps2_gxemu handles them well. With the patch to render at 640x448, it stacks on top of the resolution improvements that ps2_gxemu automatically does. Combined with the smoothing filter, the edges of 3d models look fantastic without any frame drops The only way to improve visual quality any further, is running the game on pcsx2 and bumping up the resolution even higher.
The CECHE/C catches shit and is less desirable/sought after for not having as great of compatibility as the A/B models, but it's PS2 emulator is a beast in regards to visual quality specifically on hi-def displays.
It's my system of choice!
Link for the patches I kept mentioning
https://docs.google.com/spreadsheet...AUpl9n1wlt3oqIxcgEC/pubhtml?gid=0&single=true