Hey there!

The plant in the second photo looks fine - that's a pretty standard color variation on cucurbit leaves. My pumpkin and zucchini plants do that every year (although not every leaf on the plant will do it, especially not the youngest couple sets). Nothing to worry about there.

Just for future reference, note the shape and location of those silvery spots - see how they're kind of a specific pattern, tucked into the angles of the leaf veins? That's normal. If you ever see spots that are more circular, or amorphous, or scattered irregularly all over the leaf, that would be a problem. The discoloration you'd see from a mosaic virus would look more like this, with random blobs of dark/light green patches and probably deformed leaves.

I'm pretty sure the first picture isn't a disease either, although I can't remember what causes that look (if I ever knew) but anyway I wouldn't worry. Just keep the plant in good health and who knows, maybe that's typical for that variety.

Those look like pretty sturdy plants for being raised under a grow light though, congrats! I hope you're planning on getting those out in the sun as soon as possible.

Thank you sunnyvalley for making my day, you truly have eased my cucumber anxiety! The pictures are 3 weeks old, they have both been enjoying the sun outdoors since then. But the growth has been slow, and I was convinced it was due to illness. I can now stay patient!