When using color pencil the lightest to white area must be planned out and worked around. You could also use masking fluid to make sure you don't accidentally cover it.
Work things lightly first, it is easy to erase light mistakes. Once you are confident of placements you can start to darken, go a little at a time in layers until you reach the desired affect/tones. White is rarely actually white. You can shade it with light touches of grey, blue, tan or even green depending on what is going on around your subject, i.e...forest or sunset (where you might even consider pinks or peach-ish).
Hope this helps.
Never forget the first rule.....if it isn't fun you're doing it wrong!
Okay, I can do this,....I am an,....arrr, ....arrr,.....artist!