Hi C.,
My daughter is 19 months old and does this all the time. She has for awhile now.
I echo the other moms ... I try to allow her as many decisions as possible during the day. I also let her help out around the house. I've found the more involved she seems to be with me, the fewer issues we have.
Also, I've noticed the times when we have the biggest issues with this are twofold: 1) when she is over tired or hungry. So something else is going on and she is just frustrated. 2) When I'm trying to do something for her that SHE wants to do.
Take your example.... your daughter said she was done. Maybe SHE wanted to put the colors away. I keep my daughters on a lower shelf in our kitchen. It's out of my way and she can reach it. She gets them when she wants them and puts them back when she's done.
I've found if I try to intervene too soon ... then we have a fit. BUT if I wait... and then she realizes she needs help she will actually come to me and ask for help. Then, there is no power struggle. I reconfirm that it's OK to ask for help ... that's what we do for eachother. She is happy, Mama is happy and our day is peaceful.