Depending upon your camera, a properly exposed high ISO image can suffer from several types of color problems. Yes, the difference can be quite dramatic depending upon the camera and how you processed the file.
It all depends of the limitations of your gear. I don't know what the 350D is capable of. If it is a consumer grade camera then ISO8000 - ISO1600 is probably your limit. The other part of the equation is the lens. Assuming proper exposure, considering each components limitations, you should still be able to achieve a decent 7x5 print, quite possibly larger.
So what do i need to do to get more dull or brighter colours in my images?
Changing ISO will change color rendition. Big changes will make bill changes.
The most commonly noticed affect of increasing ISO from the base ISO is an increase in noise. This distracts most forum conversations on the effects of ISO change away from the more subtle color and tonal changes.
At higher ISOs there is a reduction in tonal range which affects the range of colors that can be reproduced. Color saturation is also affected but automatic tweaks are generally applied in an attempt to compensate. This works well, but still doesn't fix the limited color palette available at higher ISOs.