Difference between underside of Den Nobile leaves

[Diane56Victor]

Hope someone can help me with a diagnosis or put my mind at rest about this.
I have a number of Nobile Dens bought from different places and on the underside of the leaves some have a silver look while others look a normal colour.
I've tried wiping to see if any colour was on the cotton pad from squashed bugs....there isn't. The silver leaves are not sticky, but it wont wipe off.
I've checked constantly for bugs there non that I can see and believe me I've looked.
All are growing well. Those with the 'clear' leaves have not changed to look like the 'silver' ones or vice versa.

[Roberta]

That sure looks like spidermite damage to me. They are very tiny, you may need a hand lens to see them.

[estación seca]

It could also be old spider mite damage. Nobile Dens. are highly susceptible. I would use insecticidal soap or 70% alcohol spray on all surfaces and the pot. I spray all surfaces of my plants every 1-2 weeks with water to prevent spider mites.

[Diane56Victor]

Spidermites - just what I was worried about!
I have on many occasions looked with a magnifying glass and hadn't seen anything.
Will take another look today and prepare the insecticidal soap, looks like I'm in for a few weeks worth of treatment.
I looked up the life cycle and found estimates from 5 to 20 days but this depends on temperature.
We are in mid Autumn here but the plants are indoors under lights.
What would be the best application plan to try and get rid of these?

[estación seca]

I would take them to the shower or outside and douse all surfaces with 70% alcohol or insecticidal soap.