I'll let the technology for color eInk develop a bit more before I look into the upgrade. I would prefer three things:
Larger screen like 12"+. Kobo Elipsa2E is 10.3"
more vibrant colors for the color eReader. Currently, the color eReaders only have a touch of color
Better 3rd party software retailer support
Lower price. Currently: $500 - $650 for a color eReader, vs $400 for Elipsa2E
A comparison video of Color vs Black & White with Kaleido 3:
In short, for just reading the B&W is better. For color comic readers or for highlighting text in different colors, the color version is better. I prefer less distractions and the better reading experience.