Create a Curves layer just above the picture layer. Steepen the curve to create lots of contrast in the cloud. On the curve layer mask, use a black brush to exclude everything but the RED clouds from the effect. Consider selectively steepening just the Red curve by itself, as well.
If that's not enough, do the same with a Hue Saturation layer until the clouds are Red In Color.
There are other ways of course, and numerous elaborations on my basic technique such as luminosity masks, different blending modes, etc. But transparency film or even Mama Nature don't usually do that unassisted, your input is required.
When you're done, sell it to a millionaire. Pictures like that don't bother them and Peter knows that all too well. Also Peter now shoots digital.