Yellow just means there are alternative scenes IIRC, not entirely different ones like green
yes, yellow means some scenes has an alternate (like doing raw or not, like Natasha's night scene) or a continuation locked by progression (GAIA or Love points)
Both of those I supposedly already cleared in Kath's contest, but even with all 6 of it's scenes completed... It's still yellow (while both Andrea and Natasha became black at the same time in that event, since I did this just before the epilogue)
My guess for Andrea's "Changing" never becoming black, was me rushing too quickly. (ie doing fancy dinner first before pool party on restrained Andrea, which led for all her 3 scenes for that to trigger... and yes I also did the brith control pill afterwards to see if it will fix it, but nope still yellow)
I did poolside first this time while Andrea is in restrained, and seems like it's now ok this playthrough.
Andrea now stopped until the thigh scene, so now I only need to wait progression until it becomes green again.
Edit:
-Yep, you should do pool party first for Andrea before Fancy dinner, and get only until the thigh sex first. (So it won't still visually show as yellow once you get to the cowgirl sex)
-For Andrea x Kath's watch tv threesome, you should also just watch them first. Before joining in the next time (otherwise it will skip the "teasing" check for the both their checklist, but will still mark their schedule as balck)
-Never found a way to make Kath's contest turn black though, No matter if I do the family boobjob scenes on or before other threesome event. It just keeps staying yellow on the schedule.