As others have said, 'blueish' is a complete misnomer, the paper actually appears gray to your eye. I have several suggestions based on your first few posts.
First, always start with the assumption that you have the most common variety because this is what you will have 99.9% of the time. If you start with the assumption that you have a rarity, your identification process will be incorrectly influenced, you will end up wasting time and effort, and ultimately you will be disappointed.
Second, if your stamp has hinge remnants and/or paper stuck on the back; soak the stamp in cool, clean water and dry flat.
Third, to check for 'blue' paper scan the stamp on an orange piece of paper and post the image here. Here is a good scan and note how the gray paper (left stamp) jumps out at you.

Don