MAP_FRAME_PEN affects the font color of the text added to the NaN box of a colorbar

[yvonnefroehlich]

Description of the problem

MAP_FRAME_PEN can be used to change to frame of a colorbar.
It turns out that additionaly the font color of the text added to the NaN box is changed.

Full script that generated the error

gmt begin cb_frame_nan_color png
    gmt basemap -R-1/1/-1/1 -JX10c/2c -B
    gmt makecpt -Coslo -T-1/1/0.2
    gmt colorbar -C -DjMC+w6c+h+n -By+lpoints --MAP_FRAME_PEN=1p,magenta
gmt end show

Full error message

No error or warning messages occurs.

Actual outcome

Expected outcome

The font color of the text added to the NaN box should be unchanged, e.g., here in black.

System information

• Operating system: Windows 10
• GMT version (gmt --version): GMT 6.6.0, dev 6.7.0_8931e47_2026.01.12