I am in the UK and have had my N64 hooked up to my Samsung 32" HDTV via RGB perfectly for a while now.
However, I wanted to move it in to the other room where I have a 42" Sony HD LED TV. When I connect via RGB, the picture quality is great but the colours are really off. It seems to be the yellows...they show up as bright white. The best way I could demonstrate it was on Mario Kart 64...the star power up was white and the beige dirt track part around the edge was a bright white colour.
I have tried every setting on the tv imaginable to no avail.
One weird thing I noticed was that when I paused Mario Kart 64, the colours were correct again! It was only when un-paused that they yellows were messed up.
It's definitely not the cable because it works fine on the samsung and also my friend's LG TV.
I am currently using the RF cable to connect the N64 to my Sony TV, which has perfect colours but of course has much less picture quality.
Any tips on a setting I may have overlooked?
I should also mention I tried connecting it via my DVD player with the exact same colour issues. Mind you, the DVD player is also a Sony...
Now my tech on TV sets aren't the best.
But the newer TVs using LCD, LED, Plasma etc cannot handle the interlacing the same way as the old big glass CRT's as they utilised a tube.
To test I would suggest using the original RF adapter and attempting to see how the picture looks that way, the only other solution I can think of is using an analog converter.
Its a little device that your N64 plugs into and then a HDMI from the device to your TV, this box basically processes the image and converts/upscales through to modern HD resolution TV's.
They can range in price from £30-300 so it depends on the features/quality you're looking for.
Hope this helps