Indeed, it is as Dark Nemesis says.
If you're using Red/White/Yellow, you're using Composite Video (only the Yellow gives you video in an analog signal). You're going to get a lot of bleeding effects, etc. since the analog signal is quite outdated these days and can only produce a certain level of 'cleanliness' in a signal.
If you were using Red/Green/Blue/Red/White, you'd be using Component Video, which is still an analog signal but now you've got three video signals (Red/Green/Blue) and two audio (Red/White), thus providing a better picture.
HDMI will give you a digital picture with no signal loss. Your video (and audio) quality should improve quite drastically provided that you have a TV that supports it, which it sounds like you do considering the model number you provided.