A friend of mine has 2 boys and is babysitting 3 more tonight - yowza!  She's hoping this activity will keep them entertained for a few minutes, but she had a some questions.  First, can you dye the dough with food coloring?  Yes.  I used Wilton gel food colorings, but I think others might work.  It is a bit messier in the mixing process but works ok.    Second, she wants to know if she should set it up before they get there.  I've had a few failed craft experiences because I didn't set up ahead of time.  Just like mise en place in the professional, cooking kitchen, you need to be prepared.  Toddlers have a short attention span & can't be bothered with waiting for anything.  I found that out the hard way!  That said, mixing the dough can be lots of fun.  She is also planning to make the super soft playdough (we have to try that one soon!).  So, this is my suggestion.  Make the super soft playdough ahead of time.  Have everything out on the table that the kids will need, ie: mats, cutters, rolling pins etc.  If they aren't interested in mixing the salt dough with you, they can always start right in with the super soft dough.  Then if your kids are around age 2, measure out the ingredients for the salt dough but don't mix them.  If your kids are older & they might like measuring, just have the ingredients and the measuring cups out on the counter with bowls, spoons etc.  For all ages, let them choose the color, but they might need help mixing in the color in order to keep your kitchen (& the kids themselves) from also turning blue, red etc.  However you do it, gather up all of the stuff you will need ahead of time so that there is no scrambling around to find things.  If you do have to scramble, you can almost guarantee at least one meltdown!