They look to be top quality. Do you know what glue Paul is using?
Paul does a great job of these, you cannot see any difference of colour between the glue & the Corian and at the price i'm getting them for I could not make them myself at this cost & they certainly wouldn't be such high quality. They are also 20mm x 20mm x 150mm so plenty big enough for the larger pens.
The ones with black Corian ie black & yellow / black & white are glued with a matching black Corian glue.
The white & blue / white & grey are glued with a matching white Corian glue