I'm using occassionally Hatari_Falcon to test productions. I found that 1.9.0 (1.8.0 neither) does not change border color in highcolor mode, when monitor is set to RGB or TV. It stands on white. The situation remains same in fullsceen mode and windowed mode. And actually in 'both' versions.
I'll run TOS 4.04 which is same as in my real machine.
Hatari is running on W10, precompiled.
-- Emphii/Extream Plain 14MB F030 with 2GB (was 4GB) CF-modification (mem from Lynxman,thx man)