Answer: There are a couple of reasons I can think of that would cause this. One possibility, especially since they are growing well, is that you planted a variegated nasturtium variety; these are currently quite popular and the blotches match that description pretty well. Another is that they are suffering from being exposed to too much intense sunlight too quickly. This would happen if they were started indoors and then set outside into full sun suddenly without any acclimatization period. The only other reason I can think of is accidental fertilizer damage, which would happen if you used a foliar feed which was mixed too strong or was applied to plants under high temperatures and in full sun. Unfortunately, without knowing the cause, it's a little hard to tell you specifically if it is a problem or not. I hope it's possibility number one!
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