But I'm not a fan of the 18% grey background. To me, the background is the same as a mat over a printed photograph. Would you use that grey as a mat color? If so, I'll just shut up.
If you click on the top level "Portraiture", you see one image. It may not be obvious to all who visit the site that it's a link. That, of course, will be moot when you have a 2nd subcategory.
In "About", I think you need to separate the paragraphs with increased line spacing for easier reading.
As to mixing color and b/w photos, I find it a bit visually jarring (which may be my limitation). BUT - I think the choice of b/w vs. color in an image is an artistic decision and I don't feel it's my place to interfere. (But you did ask so I answered.)
I use a small laptop (13.3" screen). The layout works well on my screen - not all do. It did not work quite as well on my 7" tablet. The spot to "drag up" to navigate to other photos was too small. Of course this could just be my browser.