Hey!
Yeah, the outline shader takes on the texture of the text at the moment, it's honestly a feature I haven't used myself so I might change it to what you want, or make it a toggle-able option for the uber shaders. If you go into "STMoutline.cginc" and change the lines
col.rgb = mask.rgb * i.color.rgb;
col.a = text.a * mask.a * i.color.a;
to
col.rgb = i.color.rgb;
col.a = text.a * i.color.a;
That should do it, I think! You might have to right click STMoutline.cginc within unity and select "ReImport" to see the change take effect.