There's pretty much two schools of thought for basing edges that I've seen.
The first is to treat it as part of the terrain on the base, in which case you'd paint it similar color to the sand/rocks, in this case a pale sand yellow. This looks great if you play on one table all the time or you've got a scenic display diorama board and your basing is designed to match the table or board.
The second is to treat the basing material as part of the model and the base as a separate element that only frames the piece above. In which case you go with something neutral for the base edges: black, dark neutral grey, or maybe a generic dark earth brown. This makes more sense if you play on a wide variety of tables or the primary display for the minis is something like a glass case or plinths, where there's no tie between the basing material and the display.
Separately, there's also the people who don't base anything which doesn't absolutely need it, and use things like clear acrylic when figures must have a base to stand up properly or to conform to game rules. The upside is that this looks decently good on every sort of table, board, or display, the downside losing the artistic opportunity for complex basing and mini dioramas. It can also be hard to do well without smearing or abrading your clear base or if the miniature doesn't have sufficient and well balanced contact points.