My blues are some of the nicest rats, and I've never noticed any issues regarding breeding for either my blues or my siamese. I think it's more lines than the actual color genes. In other words "Bob's Blues" might have issues, but not all blues... same for Siamese... "Kate's Siamese line" might be aggro, but not all siamese.

The closest I've had to an issue was the siamese sometimes grab a finger when I open bins because they think I'm handing out treats. Only my siamese and albinos ever seem to do this. The rest 'see' it's a finger. I think this is the red/albino eyes having issues earlier, since it's also only older rats, not the younger albinos or siamese.