Of course, the Raven Guard have no official set of veteran markings or any such thing. Shrike's markings are pretty much personal taste and there are examples of variations with Captain Solari and other Veterans shown in artwork. Plus with no real deffinitive statement on squad and company markings, and with the codex dictates suggesting regular change in such things you can do pretty much anything you want.
Plus despite being all black the common idea that it makes the scheme dull and boring I find rather unfounded. Just as hot pink and green don't make a scheme interresting, black isn't necessarily a bad thing either. With the different color trim on the right shoulder pads for squads (red=assault, green=tactical, yellow=devastator), and then whatever you do to mark company and unit designations, not to mention any scrollwork, personalization, campaign markings and so forth, you can make a pretty interresting and characterful scheme.