I want to make some concrete planters- can I mix paint in?

I wouldn't try paint with it but the powder colours you get for grout should work

No, it's not a good idea to add paint to concrete mix as it will affect the chemistry that takes place when the concrete cures. Rather add some type of pigment, usually sold in powder form.

Do not mix paint in your concrete. Get powdered color especially for concrete at your building supply store.

Large retail outlets have powder for coloring cement.However, you can use latex paint to color your project since it is water based.You would need a darker pigment in order to make the diluted version the desired color.

Unfortunately its not a great idea but you can use a concrete stain afterwards to give a similar affect- I love Unicorn Spit for example

Unicorn Spit is a great choice. Agree with Hillela

Yes, I have done this. It's easier to get the color for cement and mix that into the cement or batches for different colors.