Ok, a few minutes ago, I had no idea about which I/O ports were related to
colors...
and now, I begin to suspect what could be wrong in VirtualBox code,
that is it seems to ignore port 0x3c6 (mask register)... which is said:
"in normal use, should be 0xff"...
In: https://bos.asmhackers.net/docs/vga_without_bios/docs/palettesetting.pdf
they explains how to directly manipulate colors...
In
https://www.virtualbox.org/browser/vbox/trunk/src/VBox/Devices/Graphics/DevVGA.cpp
For write: line 616-640: no 0x3c6 between 0x3c5 and 0x3c7.
For read: line 503-507, no 0x3c6 between 0x3c5 and 0x3c7.
Not sure how much I am on the right track with that.
Might compare with what dosemu2, or qemu does, to see if they do something
about 0x3c6.
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