Cattleya labiata var. rubra '#2'
 

It is common seeing dark Cattleya labiata flowers labeled as variety 'rubra' that a closer examination reveals they are not. There's a precise definition of what a variety rubra should look like in Cattleya labiata (and by extenstion in the other labiate Cattleya too, I suppose!). Rubra is the flower having a dark purple, almost red color in the sepals and petals, way darker than the type and no white areas, except for the column. This has a special meaning for the lip where no white should be seen. A rose color in the 'eyes' is tolerable and don't eliminate the flower.
By the definition, flowers simply darker than the normal, but having white areas are not true rubras as is common to see labeled out there.

Here's a true rubra:
Cattleya labiata Lindl. - var. rubra '#2' on Flickr - Photo Sharing!

And below the rubra compared to the type:

Wow! I'll probably never remember that when I buy another cattleya, but wow! Thanks