Here are some bush peas and chard with odd discoloration on the leaves:
What's going on here, and how do I fix it?
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This appears to be leaf miner. Here is an RHS page about leaf miner on beets. Probably the damage is done to these leaves but the adults have moved on to other things. Remove any leaves still showing signs of mining and destroy to interrupt the life cycle. Watch carefully for repeat mining and remove affected parts, but as already noted the plants should survive quite nicely after the temporary setback.
This looks like sunburn. If the plants were first grown indoors behind a window, and then directly planted outdoors in full sun, the leaves were not ready for this strong sunlight yet and got burned. You can try to acclimate your plants first next time, by putting them only a short period of time in the sun and built up the period over days.
Like @Jurp already nicely noticed, is that your new leaves are green and healthy. They are developed in full sun and are okay with that. I would just let it grow now and leave the affected leaves on it, the plant will get rid of it by itself in time.