I think I've found out: 

pattern: For figure (f) even, there are more f gray triangles than white ones.  

| 1 | 2 | 3 | 4 | 5 | 6 | 7 |
|     :---:      |     :---:      |     :---:      |     :---:      |     :---:      |     :---:      |     :---:      |
| 1 | 1 | 6 | 6 | 15 | 15 | 28 |
| 0 | 3 | 3 | 10 | 10 | 21 | 21 |
|    | +2 |  | +4 |  | +6 |  |

Total triangle = 62500

62500/2 = 31250

gray = 31375
white = 31125

50,2%

0xbitcoiner

I seem to have missed the pattern of gray in the even figures, I've expanded the pattern and verified that it doesn't exist. Now I'm confused!

Can you elaborate on c? Don't think it is correct...