I would like to set up like this:
- IF variation = Color THEN show "thumbnails images"
- IF variation = Size THEN show Size text (not "thumbnails images")
Depending on what plugins you're using to show them as image thumbnails, you can set each attribute (under Products > Attributes) to have a type of image, label, text etc.
If you go into the edit screen for the attribute and see if there's a drop down to select a type other than image, that's the best place to start. If there is no option to change it to something else, then have a look at free plugins which will add other options (there are loads).