You go to the 'About Me' section in My Gaia, then type in: [color=(here, you put the desired color, like hotpink or skyblue, or green or orange or whatever you want to.)[color] So, it would be like:
[color=hotpink] This is an example. [/color]
To change the font size, you put [color=hotpink] [size=12] This is another example in hot pink. [/size][/color]
You can mess around with the font size and color. Just remember to click 'preview' before submitting, because it might not have turned out how you wanted it to.