Let me make this clear before I describe the screenshot: This livery for Diesel is PRIVATE. Apparently it won't appear in Sodor: The Modern Years since it was part of some poll about Diesel getting a new livery or sticking to his usual BR Black livery. It was distributed to me by WildNorWester himself as thanks for testing and providing feedback on his various models that are yet to be released once S:TMY continues. I thought the new livery was a great idea since Diesel is now NWR property. The way his livery was painted on looks very much like Derek if you ask me.
Now for the description.
Diesel was offered a new livery for working so hard. He accepted since it felt dull being coloured black all the time. However, after being repainted, he didn't feel so sure about it as he worried others would laugh at him (he's sort of right there). Upon returning to the sheds, Patrick complimented the livery, but Diesel still felt somewhat disgruntled as he thought that worse was to come.
Models and Route are by WildNorWester.