>>What is the red angle?<<
The red angle will not help you compute it.
The yellow angle is not 95 degrees it is 96.54 degrees. I computed it.
>>What is the green angle?<<
It is 90 degrees.
Try connecting G2 with the other diagonal point at G3. All you need to know is that all angles in a triangle add up to 180 degrees, and use the formula:
a^2 + b^2 - c^2 = 2 x a x b x cos(A)
a, b, c sides and A is the angle opposite to side c.