[Change colour of object]

Affinity newbie here and hoping someone can help please. I've created an outline of a campervan, but I'd love to change the colour from black to blue. Is there a way I can do this or can you not change a background object? There's various objects as my initial selection wasn't perfect so I'd need the right wing mirror and campervan changing. There is also a rectangle under the windscreen which it lets me change the colour on but I can't work out anything further. I'm a Mac user.

Thanks, 
Charlotte 

campervan outline BW.afphoto