1- Is this really worth it? If all she really wants is to wear the clothes she picked out that don't match at all, then No, the ensuing tantrum is not worth it. Clothes that don't match never hurt anyone. However if it is something like not wanting to brush her teeth, or hitting some one then Yes it must be dealt with now.
2- Am I angry? If I am angry I need to take a moment to calm myself before approaching her. Discipline through anger teaches her fear, not correct behavior. Mommy time outs are a good place to go from here, before disciplining her.
3-Is this really not a discipline lesson, but a power struggle? If I feel myself about to say "Because I told you so." or truly getting aggravated over the choice of mismatched clothes, it is probably a power struggle.
Redirection is a common discipline technique with little kids... "No you may not play with the blinds or jump on the couch, but you may play with your blocks or jump outside or on the floor." I think perhaps it is also a good idea to redirect my energy as mom when things come up. Since I am in need of reminding sometimes, I wrote a list to help me redirect.
Things I would rather do than engage in a power struggle with my child:
Read the Bible
Read another book
Breathe deep 10 times
Give a bear hug
Sing a silly song
Go on a walk
Eat a cookie
Get a box of stuff ready to donate
Dance to the radio
Look at my garden
Make a gift for some one else
Drink hot tea
Go somewhere else - the park, the museum
Take a relaxing shower
What redirection techniques do you use for you?