Thank you, you are right, and we checked it against our own source. The marker asks whether a named partner exists, not how many bloom days the two trees share. An early tree beside a mid tree shares two of its five days, so it sets 0.4 of a crop while the cross shows green, and a crab beside it would set 0.5 while showing amber. So green can rank the worse partner first, which is the opposite of what the marker is for.
We have passed it to the team that builds Crossbloom with your suggested fix: score the cell by the share of the tree's bloom days that have a partner, or draw a partial overlap as amber. We will reply here when a fixed build is live.
Thanks too for the note on the frost timing and the lonely warning.