So, I'm planning to make a Moderne Log Cabin Blanket, (only with crochet rather than knitting, it being an easy conversion in this case. While using a tad more yarn, it will be so much quicker that it is worth it), and found a fun and easy way to play around with potential colour combinations.
Having downloaded the pdf in question, I right-clicked and saved a copy of the layout pictures. Now, using GIMP Image Editor, I erased the colours, and saved them as log cabin blanks. Since I'm ordering Knit Picks yarn for this, (I decided to move up a size to worsted weight, going with Wool of the Andes worsted), I could also save copies of the pictures of each colour of yarn that I was considering.
Rather than cutting and pasting bits of these pictures, I instead used a simpler option; I copied the pictures and saved them as new patterns. All I needed to do now was use the fill tool, and play around with all the different combinations. I can't help but think that it would be even cooler if the source photos were of swatches rather than skeins, but it does nonetheless provide the variations in shade and texture that make it look like it's made of yarn rather than flat paint, and makes it much easier to decide between subtly different shades. I'm not sure what other graphics programs will allow for the same ease of use, but I do enjoy tinkering with GIMP Image Editor, and really enjoy finding more knitting and crochet applications for it.