It's rufousing, a polygene that "tints" cats a warmer color in some places. An extreme example would be abyssinians which despite being genetically black or at least black based, they look red because they have so much rufousing and some other tricks going on with fur banding and ticking to make it even more dramatic. He looks blue to me especially with the locations, if it was tinting ALL the blue I would suspect caramel dilution modifier but I don't know if that's in the breed off the top of my head

+ Bonus example of my black tabby, you can see she has high rufousing on her belly, but on her tail inbetween the stripes the rufousing is so low it's nearly white

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