I tested both colours on a test subject. The section of the left wing outboard of the 20mm gun is in AMT-1 and the inboard section is A-21.
The differece is imperceptable in my eyes.
It was in response to Learstang's comment that the A-21 looked too grey and apparently AMT-1 should be more tan.
I was about to post I'd just noticed AKAN now do acrylic AMT-1 when i thought I had better check if this had been mentioned, and I found this.
And tyronesdaddy does mention that the paint is acrylic.
From this photo, the AMT-1 does look more tan than the A-21 to me though.
T