Photoshop Question

[Bennett]

I have a simple little painting that I did a while ago that I want to scan onto a computer and manipulate.

My question is, how difficult would these manipulations be using photoshop or similar software?

Here's the situation,
The painting contains these colors:
-a mix of dark blues
-a light purple
-a light pink

I want to
-change the blues to shades of gray
-change the purple to a dark gray
-turn the pink to a pale yellow

Would this be easy, difficult, possible?
And should this instead go into the art forum?