Why are some of the color previews such strange colors?
The best-looking color images use a combination of three colors that are well spread out in wavelength. A common example is F435W (B), F606W (V) and F814W (I). However, in most cases the available filters used to make the color preview images were not selected to make a “pretty picture”, hence the spacing is not optimal and the resulting color is sometimes not very good (e.g., a F435W + F775W + F814W combination). Another example is when only two filters are available, so that the middle color used to provide the green image (in the normal red-green-blue or RGB method of making color images) is populated by combining the blue and red colors. Hence there are not three independent colors. These do not always provide very pleasing color images. Still another example is when the WF4 anomaly is present for chip 4 of the WFPC2 (i.e., data from the past few years where the bias level has been suppressed). The non uniformity of the image leads to a wide range of colors from the color lookup ta
