From what I can see, both R1900 and R2000 use "Ultrachrome Hi-Gloss2" ink, and the colours might be the same from the Epson description (Gloss Optimizer, Orange, Red, Magenta, Yellow, Cyan, Matte Black, Photo Black) although I don't know if they are in fact exactly the same colours. However, the R2400 uses a different ink set. It's described at "UltraChrome K3", and the colours are different (Cyan, Light Blank, Light Cyan, Magenta, Light Magenta, Matte Black, Photo Black and Yellow - no gloss optimiser, and IMHO very probably a different ink formulation).
I found one web site that appeared to suggest the R1900 and R2000 might not use all the same inks. See
http://www.marruttusa.com/printer/co...inks-chart.php
and
http://www.marruttusa.com/printer/co...inks-chart.php
If I read this correctly, only 5 of the inks are the same, but maybe I misread it.