Color vision deficiency is a common affliction for males, impacting about 8% of the population. The effects of this – colloquial – color blindness is the inability or limited ability to distinguish colors. A typical problem might be that a color changing LED, changing between red and green to indicate two states, will not be differentiated. There are multiple ways to detect and distinguish color deficient people, ranging from genetic testing, to simple pseudo-isochromatic charts, as exemplified by the likely most known Ishihara charts, to elaborate color matching and color sorting tests, as exemplified by the Farnsworth-Munsell 100 Hue test. In this talk describe initial experimental data on changing the background color – or the color “in between the dots” - for a pseudo-isochromatic chart color deficiency test. For the experiment, we replaced the white background with 4 different neutral gray-level values and measured the performance of known color deficient observers on these charts as a function of the new background. Though preliminary, the data show a significant difference in the performance of color deficient observers, despite the main pseudo-isochromatic colors staying the same.