You need to be a bit geeky, but if you export your settings, it's all there. Text for each airspace is RRGGBBTT (where TT is tranparency), in 00 to FF in hex for each channel. FF for transparency is opaque. Text is "Color3" under each airspace. Color 1 is the solid line, Color 2 is the secondary color like the shaded inner border (depends on the airspace type).
For instance, here is the default Class B definition:
airspace_class_b={
color0=004AB4FF
color1=004AB47F
color2=0058D6FF
width0=2
width1=4
cycle=0
fraction=0
outline=0
style=MAP_BLING_DRAW_STYLE_SOLID_FADE
}
"color2=0058D6FF" is the text color.