Sounds like powdery mildew. Can't get rid of what's there.

Beyond that, it's the end of a coleus' life at this time of year.

Well my coleus are indoors.

Try a spray of either 1 teaspoon of baking soda mixed in 1 quart of water, or a 50/50 mixture of fat free milk and water, and spray the Coleus every 5 to 7 days and see if that helps.

OP said "Well my coleus are indoors."

Thanks.

As said, it won't get rid of it. When it comes to the suggested homemade sprays, they *might* slow the infection rate on the new leaves, or not.

It may still be the end of your coleus' life. So if you have "clean" stems, you might grab some cuttings and root them.