In Sketchup you only get the R,G,B edges on objects if you have that option turned on in your settings and the edges are parallel to the X (East/West), Y (North/South) or Z axis. There is no visual clue for just right angle or horizontal. But it was originally thought of as a visualization tool for architecture so right angles and compass headings are built into its bones.

When you draw a line or rectangle though, or pull out a construction line, after your first click, you get a thin line that matches R, G or B when you are parallel to that axis until you make your second click. This is necessary for Sketchup since you are always working in 3d space. There is no defined rule about drawing only at Z=0 when you are normal to the X,Y plane. So it can be a very small mouse adjustment between a second point that is vertical (blue preview) and a second point that is North or South (green) depending on where your camera is. You can click a button and put your view into front, top, right, left, back or iso views and you can set your camera to ortho or perspective.

It is like anything, it takes a little practice but once you are used to it you can really pump out the drawings.