Take a look at the Style Table.
These are styles that are used by various designobjs in Designer, and what Orbiter uses to paint everything.
These styles have variations.
Look at the StyleVariation.
See the references to FK_Style? Those reference back to the styles in the Style table.
See FK_Skin? If a number is here, then this style variation is for this given skin. If it is NULL, then it is a fall back for all skins.
So what YOU need to do, is to start adding rows for the individual styles, for your skin. You'll probably add one for each style, except where FK_Skin already has a number. we have some styles specific to the Mobile Basic skin, so you won't need to add those.
If you look in each row, a font is specified.
A quick note about colors:
You'll see references to foreground and background colors, with weird numbers. These are the decimal form of web colors, so take a paint program like GIMP, get the hex number there, put it into a calculator as hex, and flip it to decimal, use that number.
p.s. Another note, once you make these style changes, everywhere you use this skin must have this font, or you will not see text.