@Aloredd Whether or not you colour it depends entirely on what the rest of the panel looks like. If it's an overall dark panel, you might want to colour it to make it stand out enough for the readers to actually see it. If it's an overall lighter panel, you can get away with having it be lettered in black.
As for whether to go with bluer or redder shades - again, that depends on context. I personally don't "hear" a difference in pitch depending on whether it's red/blue; I tend to pick my colours depending on the surrounding colours, and what the sound is actually representing. If it's a loud explosion, for example, I might go with red - because red implies heat. If it's ice cracking, I might go with more blue shades. If it's a rustling in a forest, I might go with green, etc., etc.
And remember that sound effects aren't just text; they're design elements, too. Where you place them, and how, makes a difference to how the entire panel is read. @scythe''s examples are excellent for this; look at that "Whoooosh"; it's readable, and clearly a sound-effect, but is laid out in such a way that it looks like it's part of the spraying water, and emphasises the "noise" it represents.
I mostly go with hand-drawn sound-effects these days. I have a hard time finding existing type-faces that look the way I want them to, so it's easier for me to just hand-draw the letters. I'm pretty sparing with sound-effects anyway, so it's not a very time consuming part of making comics.