The answer has to be no - my knowledge of pressed glass is limited, and even more so with regard to these iconic paperweight subjects from JD - although other people may have information which might throw light on the question of applied paint. I don't recall seeing anything other than either clear glass or solid black examples, and must admit I've never owned or seen anything painted from Davidson, so I've nothing to compare these with.
As we know, after Albert's death Victoria became obsessed with black, so the suggestion is a possibility.
My opinion would be that this 'black paint' has been in place for a long time - despite being stubborn to move, there are areas (the high spots) where the paint has been worn away, revealing the clear glass. The breasts, arms and knees show this more than elsewhere, and the ridges on the plinths have suffered likewise.
Slack says that pieces bearing both the JD trademark and Rd. lozenge belong to the period 1873 - 6 only - which was the four year duration of John Derbyshire, and although there may well have been prominent deaths that might have produced a mourning colour such as this, the only obvious occasion that comes to mind is 1901.
This is certainly some time after these pieces would have been made, so perhaps this pair might have been painted by their owner on the occasion of Victoria's demise - I'm not aware of any comments in my books suggesting the existance of painted examples - so let's see if the pressed experts can come up with any reliable information on this subject
P.S. Sorry to hear of the vandalism of your Davidson pillar vases