does a bigger screen resolution slow down your computer?

Answer 1

Technically, yes.

More screen space = more things on screen to render at once, = slower processing speed.

You'll notice it a lot more in games than you would just working with your desktop. As already mentioned, modern video cards do a good job of rendering basic 2D things like a desktop so there shouldn't be many issues there.

Answer 2

It could if you do not have an adequate video card. Usually if you have a higher resolution and the card is not handling it, it will default to a lower color saturation. However, in todays computer market the cards should all be fine for what you need. In any case, worse case scenario, you get a new graphics card to handle the better monitor.