The thought process or reasoning behind pairings

[bks2100]

Part of the "game" seems to be Bold is Better, so it makes sense that the first thing into a new morph is something to crank up the brightness. I think it's pretty intentional - you crank it up a level with Pastel, and then you can double it with super Pastel... other common enhancements seem to be Fire, Vanilla, Enchi. Or on the darker end of the spectrum you've got Cinnamon and Mojave - those Mojave GHIs are no joke!

There are a bunch of morphs that can darken or lighten others, I'd say the reason pastel is so prominent is just because it's older than most morphs, it pretty much always has a positive impact on other morphs, and it's a co-dom that has a super that doesn't mask anything. Pastel is just super predictable and super reliable for combining with other morphs. Not to mention pastel looks so much nicer as a hatchling so it helps sell new morphs.