Re: calligraphy???
Yaar making different colors is not too hard once you get the hang of it. Once you start painting, you can make colors lighter or darker depending on your mood. Like for instance, lets say you wanna make chocolate brown, mix green and crimson. If you think its too dark, add a little white to it, if you think its too ‘browish’…add other color to it such as orange/yellow etc etc…just experiment and see. You’ll learn it good that way 
I just choose colors as I start doing the painting. If I don’t like something, I just wipe it off and do it again (which won’t be possible in Acrylic since Acrylic dries within 5 minutes and you end up loading the palette with colors over and over).