The colour of vector artwork is controlled by the colour associated with the vector layer. The default colour for new vector layers is black. Giving a unique colour to each layer can make it easier to identify where vectors are stored in the model, and what they are used for.
To change the colour associated with a vector layer:
next to the vector layer. The layer's Colour dialog is displayed.
Click and drag the circles on the colour wheel and colour square;
Specify the colour's red intensity (R), green intensity (G), and blue intensity (B), or it's hue (H), saturation (S), and luminosity (L); or
Click and drag the pipette to a colour on the screen, then release the mouse button.