While watching a Korean shows about a disabled guy that could play piano. I realized how I, and others like me, could develop perfect pitch....without any gimmicks!
First, we'll take the key of C. Most pianists start in this key, and it's the easiest to use as a pitch guide for the rest.
In other parts of the world, scales are taught not by numbers but by the sounds. It's a little weird to get used to, but we all were taught it, even in the United States, but we didn't know it....Have you ever watched the movie, "Sound of Music"? If so, then you'll know where I'm going next.
If we number the C scale according to the pitches, we'll have the following:
C - Do
D - Re
E - Mi
F - Fa
G - Sol
A - La
B - Ti (or Si)
Now, using these, and your keyboard, you can practice the sounds of the key C. Just use the key of C to practice the sounds and you'll slowly start to hear all the in between relatively. Slowly, it'll all become automatic. It's working for me!
If this works for you, let us all know.