Text Color in Adobe Express

When you have a text box highlight the text with your mouse, like you would in many programs. Then choose your colour from the Swatches or you can go to the Custom tab and use the pick from there. 

To change the background colour select the whole text text box - I usually find this easier by using the layer on the right - and scroll down to Shape.

Change the shape and fill with the controls in the left-hand panel.