The capacitors are on the RGB cable. I was talking about inside the SNES. It needs 75 Ohm resistors from the amp to the pins. http://retrorgb.com/snesminisrgb.html
Its strange that only Yoshi’s Island is washed out but Zelda in the sewer and Metroid are supposed to be quite dark aren’t they? The only other difference that I can think of is that Yoshi’s Island uses the FX chip which draws more power. Are you using an original power supply?