You can switch the black keyline on or off using the eye icon alongside the layer. To try a colour other than black, hold down Ctrl/Cmd and click on the keyline’s layer thumbnail. Now click on the foreground colour swatch in the toolbox, and either mix up the colour you want in the Color Picker or click directly on a colour within the image to sample it. Press Alt+ Backspace to fill the keyline with the new colour. You can also change the text colour if you like: double-click on the text layer thumbnail (the ‘T’ icon), then click in the colour box in the Options bar, mixing or sampling a new colour in the same way.