As far as I know, color pages are always front-loaded or the entire manga/doujin is in color. This is really about the former case. And it's just about always the case that they color the most intense moments (as it should be). But this tends to really screw with the chronological order of the story.
Of course I know that this is done in other types of storytelling but I think in hentai it doesn't work all that well. At least it doesn't seem to work very well in most cases. In hentai we spend at least a few pages getting to know the characters. If you like vanilla content, it might be some build where you see how two people converge in some kind of sweet harmony. Or for netorare it might be about how a couple might become vulnerable and seeing that vulnerability get attacked. Or if cheating is on the menu it might be about how someone made a slip of judgment. These are all key elements of story and add important context to what we're reading. Yeah it's porn, but I think it's safe to say we come here because our porn isn't purely watching the act.
So what happens is we get these great money shots in color but they're completely out of context. The characters might be nice to look at, but it happens before you're given an opportunity figure out what's going on. You don't know who you're looking at, how they ended up there, or the depth of their emotions in that moment. You can basically only appreciate the artwork until you read further. Then you come back after to read it once again, in context. But sometimes what I find at this point is that it was forced into the beginning of the story so it doesn't read particularly well mid-story either.
I'm sure it's done for a purpose. Probably to catch eyes or something. And I know that you can just skip back to the beginning or whatever but I think it takes away from the experience. This isn't a complaint or anything, just sharing my observations for discussion.