To change the color of a layer (shapes and texts), you can:
Select the layer (in the Layer List on the left, or directly on the canvas)
Click on the Design tab (at the top of the Property Panel on the right)
Change the value of the Color property in the Property Panel.
The Color field supports the HEX format.
Alternatively, you can click on the thumbnail of the Color property, and pick the color visually with the Color Picker.