Minor Description
A color with alpha value which is darkened through TerraTheme.darken(Color) looses its alpha channel. This happens eg. with the borders around a TextArea. As a result, you cannot currently have a TextArea with transparent borders.
The same applies to TerraTheme.brighten(Color).
The error is in TerraTheme.adjustBrightness(Color color, float adjustment). It creates a new Color instance but invokes the wrong constructor so the alpha channel gets masked out.