There's a closed pull request on the mblaze repository

mcolor: Add coloring support for diffs
https://github.com/leahneukirchen/mblaze/pull/249

Description:
Add coloring for diffs sent as part of the email body. This adds support for the following three ENV variables:

- **MCOLOR_DIFF_I**: For (I)nserted lines.
- **MCOLOR_DIFF_D**: For (D)eleted lines
- **MCOLOR_DIFF_R**: For file (R)anges

Since the default theme is quite bright, these default to bright colors as well (Green1, Red1 and Yellow1 from the 256 XTerm colors respectively).