In my opinion they are not 361. The paper would be a uniform gray; it is not the grey shading (lighting artifact) we see in the lower parts of your stamps above. Classic paper is correct, the odds of stumbling upon an undetected 361 are smaller than seeing Big Foot and dating a super model on the same night. Assume that you will always have the most common varieties because that is what you will have 99.8% of the time. But you can always spend your money and send them to a certifying organization if you want to be sure. Don
The dark color of the ink of the design may be fooling your eye. If you look on the reverse, where there is no offset and no design on the other side, you can see that the paper is 'white'. Bluish paper stamps are distinctly and uniformly darker than what you've photo'ed. Fakers have tried dying these stamps to get the blue-gray paper, but it always looks fake - wrong color and not very uniform. Your's don't look fake, but you may run into some that you can see are a different color and ASSUME they are the bluish paper - don't get fooled.