To change bubble and text color, first clicktap inside any bubble.
In the editing menu,
The tabs on top determine which part of the bubble is affected by the palette. The Bubble color tab contains the bubble color palette, and the Text color tab contains the text color palette.
ClickTap on the colored squares to preview your bubble and text colors.
When you're satisfied with your color selection, clicktap anywhere outside the color selector, or press Escape key.
To chose a color different from the pre-selected color palette, click on a custom color button in the bottom-right corner of the color selector.
You can use Hue/Saturation/Saturation sliders, or a web-style hexadecimal RGB field to choose your color.