I really hate to necro this, but does anyone have an answer?

Well that explains a lot, I have installed a few mods that all wanted to use the startypes.xml file and decided to go with the HRGM file, which might be corrupt.

Also, could the stars.fx file have anything to do with it?

Yeah, I have a custom Stars.fx file in the mods folder...

I have noticed a lack of purple stars in my galaxies...could it just be those?

xml file contents:

<?xml version="1.0" encoding="ISO-8859-1" ?>
<StarTypes>
    <DataChecksum NoParse="1">
        <Ignore>Texture,Halo,F_StarColor,F_LightColor</Ignore>
    </DataChecksum>
    <StarType InternalName="Blue">
        <Type>6</Type>
        <Texture>BlueStar.png</Texture>
        <Halo>BlueStarHalo.png</Halo>
        <F_StarColor>0.0, 0.2, 0.5, 1.0</F_StarColor>
        <F_LightColor>0.0, 0.2, 0.5, 1.0</F_LightColor>
    </StarType>
    <StarType InternalName="Purple">
        <Type>5</Type>
        <Texture>PurpleStar.png</Texture>
        <Halo>PurpleStarHalo.png</Halo>
        <F_StarColor>0.5, 0.0, 0.5, 1.0</F_StarColor>
        <F_LightColor>0.5, 0.0, 0.5, 1.0</F_LightColor>
    </StarType>
    <StarType InternalName="Orange">
        <Type>4</Type>
        <Texture>OrangeStar.png</Texture>
        <Halo>OrangeStarHalo.png</Halo>
        <F_StarColor>1.0, 0.5, 0.25, 1.0</F_StarColor>
        <F_LightColor>1.0, 0.5, 0.25, 1.0</F_LightColor>
    </StarType>
    <StarType InternalName="Red">
        <Type>3</Type>
        <Texture>RedStar.png</Texture>
        <Halo>RedStarHalo.png</Halo>
        <F_StarColor>0.85, 0.0, 0.0, 1.0</F_StarColor>
        <F_LightColor>0.85, 0.0, 0.0, 1.0</F_LightColor>
    </StarType>
    <StarType InternalName="Yellow">
        <Type>2</Type>
        <Texture>YellowStar.png</Texture>
        <Halo>YellowStarHalo.png</Halo>
        <F_StarColor>1.0, 1.0, 0.0, 1.0</F_StarColor>
        <F_LightColor>1.0, 1.0, 1.0, 1.0</F_LightColor>
    </StarType>
    <StarType InternalName="Green">
        <Type>1</Type>
        <Texture>GreenStar.png</Texture>
        <Halo>GreenStarHalo.png</Halo>
        <F_StarColor>0.0, 0.7, 0.0, 1.0</F_StarColor>
        <F_LightColor>0.0, 0.7, 0.0, 1.0</F_LightColor>
    </StarType>    
    <StarType InternalName="White">
        <Type>0</Type>
        <Texture>WhiteStar.png</Texture>
        <Halo>WhiteStarHalo.png</Halo>
        <F_StarColor>1.0,1.0,1.0,1.0</F_StarColor>
        <F_LightColor>2.0, 2.0, 2.0, 1.0</F_LightColor>
    </StarType>
    <StarType InternalName="Sol">
        <Type>7</Type>
        <Texture>YellowStar.png</Texture>
        <Halo>YellowStarHalo.png</Halo>
        <F_StarColor>1.0, 1.0, 0.0, 1.0</F_StarColor>
        <F_LightColor>1.0, 1.0, 1.0, 1.0</F_LightColor>
    </StarType>
</StarTypes>

I'm not familiar with the graphics side of the game, but the xml you posted seems fine.

One question though: Is that the Startypes.xml from the HRGM? I'm currently taking a look at the one from HRGM v2.0, and that uses different values than the ones in your post.

Also, have you removed the Star.fx at one point? Did that help any?