Plant viruses usually (although not always) produce mottled, striped, mosaic, or speckled patterns. Purple leaves and yellow leaves can be a general sign of stress or of a nutrient deficiency (or, in some cases, leaf burn from too much nutrients).

* Are your plants on heat mats?
* What are your air temperatures?
* Are your plants covered?
* Are these plants indoors that you started from seeds? If so, why are you worried about thrips - have you seen thrips?
* What's your soil look like, and how have you been fertilizing?

Don't trash the plants until we figure this out. Do you have any photos?

IMHO, viruses are often "pretty diseases". They can make your plant look neat or unusual as they kill or maim it. Random examples:

The tomato spotted wilt virus:
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Cucumber mosaic virus (closeup; from a distance, it looks like speckles):
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Plum pox virus:
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Squash leaf curl virus:
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Barley yellow dwarf virus:
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Etc. As a gross oversimplification, if the disease looks pretty, suspect a virus. ;)