Partially correct.

The Blue Grass pattern was not created by selective breeding of other grass color but through selective breeding of snakeskin with another strain which I'm trying to guess as well because not much was documented. The Grass pattern was created by Japanese.

Yes you would end up with varied colors of grass and also other varieties depending of the source of your grass guppy. I've known people who crosses blue grass with blue tuxedo to enhace the blue color of the grass and to add fresh genes into the much inbred guppy. So when these other genes are injected, it will be certainly shown in their offsprings once the genes matched/sequenced. And this calls for understanding of the genes - dominant, recessive, co-dominance etc. The other thing to consider would be the deterioration of the grass pattern. Grass is defined as fine dots. If not given due selection on the breeding pair, it can deteriorated into leopard pattern meaning bigger dots, or broken lines as a result of joined dots. Worse case scenario is turning into a mosaic pattern which is not desired in a grass guppy. Anyway all this are for high end breeders like myself. Given the difficulty to maintain a grass strain, I opted not to keep them seriously rather using it as a tool fish to create my signature strain