Likely they were badly stressed and dried out from sitting in the sun in tiny pots with no water.
You seriously set them back, but yarrow are strong, likely they will live but be stunted for the rest of this year and perhaps even into next year.
If you can, I would buy another yellow and place it with the 2 sick ones....maybe next year you will see something.
Linda C

actually, they seem to be doing better...i've even seen some new blooms. we have had almost 2 weeks of rain, but the sun over the last few days seems to have helped them. thanks for your help

It can help to cut back the stems which have flowered to about an inch from the ground.

Before you plant out - pop the punnet or whatever into a bucket of water and wait for the bubbles to stop. Bring them out and let them drain while you make the planting holes. Generally, it would do no harm to let them soak in a dilute solution of a mild fertiliser.

If you have a choice, buy the plants which look healthy but which haven't flowered so young. They put their efforts into growing vital roots and leaves instead of recovering from a burst of flowering. When they do flower, they'll be well-established.