As you know the default reCAPTCHA API theme is red, which does not coordinate with the color scheme of Prosilver or Subsilver2, the default styles packaged with phpBB3. Many people who use either of these two styles and the reCAPTCHA wish to change the reCAPTCHA colors to match the style. It would be better if they were cohesive to start with. I propose changing the reCAPTCHA theme for both styles to "clean" which is much more aesthetically pleasing than the default today. See images below:
Prosilver would go from this:
and Subsilver2 would go from this:
I believe the images demonstrate how jarringly out of place the default reCAPTCHA red theme is with both of the included package styles.