[IME]CursorColour does not work with specific BackgroundColour

[experimentlain]

When I enable IME, the cursor color does not change with the configuration below:

BackgroundColour=  7,  54,  66
IMECursorColour=   0, 138,   0

but it works with this config:

BackgroundColour=  7,  54,  66
IMECursorColour=   0, 139,   0

I attached .minttyrc to reproduce the problem.
I am using mintty 2.3.6 x86_64-pc-cygwin on Windows 7 x64 and MS Office IME 2010.
minttyrc.txt

[mintty]

Did it work with any earlier version of mintty?
How can the problem be reproduced? (Advice on IME download/activation, please)

[experimentlain]

I tried 2.1.5 and it does not work.
About IME, I do not know handy one, but Google IME (https://www.google.com/ime/) may be easy to install.

I glanced over mintty code, and probably I found the reason. In win_text() function in wintext.c:

bool too_close = colour_dist(cursor_colour, bg) < 32768;

if (too_close)
  cursor_colour = fg;

this code corrects the cursor color to the foreground color, if the cursor color is "too close" to the background color. I tried commenting out this code, and my .minttyrc worked well.

This behavior may be an intended one, but I think this is too strict at least. I do not think colors (7, 54, 66) and (0, 138, 0) are "too close". About the color-contrast problem, I think it is the most simple to leave it to the users.

Edit: this problem applies also to CursorColour. so you do not need to install IME. I put another .minttyrc to reproduce the problem.
minttyrc.txt

[mintty]

I have significantly reduced the minimum distance that triggers this behaviour. That restriction could arguably be removed at all, but the code has been in place for so long already...

[mintty]

Tweaked previous patch. Minimum trigger raised again (although lower than before) but "brightening" the cursor colour rather than just changing it (algorithm was already in use for brightened ANSI colours).

[mintty]

Released in 2.4.0.