Inconsistent

I LOVE sticker mule and use it exclusively for my art on t-shirts ! But recently everytime I get a tshirt it’s printed different … same art but it’s either too blue, too bright, too dark , too big ?? I’ve only had one order that I was so dissatisfied that I asked them to do over and they re-did no questions asked and sent them right away no charge.. which I was very impressed with!