Look at the color of the cluster, though. Almost all the stars look blue. As if. The B-V of this cluster is 0.74 according to Sky Catalogue 2000.0 Volume 2. A color index of 0.74 is yellower than the Sun, and yet this cluster looks
blue. At best, a dozen stars here appear orangish.
The reason for the truly bad color balance is that the image was taken through two different filters, F814W (near infrared) and F606W (orange), coloured red and blue. So two long-wavelength, "red" filters were chosen to make the image, and then picture taken through the infrared filter was colored red and the picture taken through the not-quite-so-red filter was colored blue!!!
But NGC 6934 is a globular cluster with a fairly typical "globular cluster low metallicity", with a (Fe/H] of -1.54. That is definitely low enough for this globular to have a significant population of blue horizontal stars. Why, then, are two long-wavelength filters chosen to photograph a cluster which contains both "red" and "blue" stars (red giants and blue horizontal stars)? There is no way you can do the the different populations any sort of justice. Of course, you may decide that colors are of no importance, and that blue stars, in particular, are of no importance, so that you don't need to identify them by using a filter that will single them out. In fact, you will barely identify the red stars either, since even the reddest stars will be bright enough in orange light to prevent
them from standing out in a picture taken through infrared and orange filters. Then, to make up for the fact that you photographed the cluster in "red" wavelengths, thereby blurring the "identity" and spectral classes of the constituent stars and particularly ignoring the blue stars, you color the whole cluster blue. Isn't that wonderful?
I don't think so!!
Ann