Hey stampavalanche.
I was like you just a year ago. Even after looking at the accurate pictures provided in this site, any 1908 definitive with an off-white color would still look like "bluish paper" to me because I truly didn't know what I was looking for. Every person on here has started out the same way, so don't feel bad about that.
Here is a piece I may have considered a candidate for bluish paper at that time:

It looks similar to yours, although mine is in much worse condition... The color of the paper has changed just enough to be noticably bluer/grayer than other 361s, but the reality is that paper can change drastically depending on a number of reasons.
Getting a cheap mint copy to study in-hand is your best bet, especially one with original gum. And your money would be better spent on obtaining one of these to increase your own experience before sending it to the people who DO have experience, then striking out.
If you get a certificate that says "not bluish paper", it doesn't really help you much.
Rule of thumb I've learned with this issue: The closer the stamp is to it's originally printed condition, the easier it is to identify.
Here is a 358 I now use for reference:


After having the experience of holding a mint example in hand, it would be impossible for me to make the same mistake as before. Not only does the rag stock change the color of the paper, but it gives the overall composition a kind of a waxy appearance, imo. The pictures from Don and Redwood are totally spot-on, but nothing beats in-hand observation if you really want to have full confidence in what you're looking for.