Prisma pencil crayons are the industry standard. I got these for my girlfriend to use, and I almost wanted to keep them myself. The lead is very soft and blends wonderfully. There is no graphite "sheen" left from pressing too hard. All in all, these will color like butter. I used them on both heavy and light weight papers and the results were excellent on both. You will easily be able to to fill in tricky spots with color!