Can't change text colors on Horos

[salgadolea]

Hi,
I'd like to take notes of my xrays but I can't make the colors pop on Horos.
In this example, when I select a yellow, the color on the xray appear very dull. For some areas, I can barely read my annotations.
What should I do?
It's the first time ever I post on a Forum, not sure what other info I should give, sorry in advance :)

Public License, Version 3 (LGPL-3.0).

Thank you so much
Léa