It helps to read both, because they use both. The Judges guide provides more of an overall synopsis of how judges should judge, and the rubric provides a very detailed summary of what they are looking for.
Judges look for the design process. If you read the rubric, more than half of it is about the design process.
Color pencils probably aren’t recommended for sketches, but I imagine if used properly, they could make the sketches easier to read and understand.
Judges use both, as the “EN Rubric” is on page 43 of the Judge’s guide…the question doesn’t make sense since the rubric is part of the Judges Guide.
An EN which is well organized, preferably in the order of the EN Rubric points, will help Judges score the notebook against the Rubric faster.
If colored pencil improves the sketch, it’s probably fine. But there might be a judge out there who is a bit AR about the “letter of the law” and want’s the whole notebook in ink no matter what.
Also, note that because of the short turn around time, the process usually goes as follows. The judges do a quick look at the ENs and place them in two piles. Those that are worthy of consideration and those that are clearly NOT. They then will go through the “worthy” pile and use the rubric to rank those.