Yellow dots on the leaves? That might be some insect. Diffuse areas of light-green that turn to areas of yellow over time might be insufficient nitrogen fertilizer, but be wary about adding more fertilizer to sickly plants! If it is insects, fertilizer won't hurt and excess fertilizer can definitiely hurt.
Can you get close-up photos of leaves? Especially close-ups of the UNDERsides of leaves, and also of the tops of plants?
If your camera has a "macro setting" or "super-macro" setting, you may be able to get really close. Other people may be able to confirm or deny yellow dots coming from insects.
Any kind of webbing indicates insects. Tiny specks or bumps are often insects,
If your plants are biggish or have a fairly dry setting (little risk of damping off), you might try giving the leaves the hardest spray you can get from a spray bottle. Spraying the undersides of leaves is more likely to knock bugs off than spraying the top sides.
If it is insects, and if someone can identify them, then you can think about spraying with different things (like insecticidal soap) or maybe taking a Q-Tip and some alcohol to bigger bugs.
P.S. If only certain plants have the dots, but the rest of them look healthy, keep it that way by removing the sickly plants from the others. That helps limit the spread of insects and some plant diseases (some of which are spread by insects).
But it might not be insects at all.
