[Wearing red and yellow under the garments]

The answer: What appears to me is that there is no objection to that, because there is no adornment in such a case and no arrogance.
And it has been mentioned in the Sharḥ from al-Qāsim, peace be upon him, that he said: “There is no harm in rugs and cushions stuffed with silk.”
And it has also been mentioned in the Sharḥ from the jurist Yaḥyā ibn Ḥasan al-Buḥaybiḥ that if something else is spread over the silk, it is permissible.
This, what we have said, is of the category of specifying (the ruling) by the underlying cause.

Source: Min Thimār al-ʿIlm wa al-Ḥikmah vol.2