doubts regarding making of color sensor

hi iam doing colour sensor using led and photo diode can anyone tell me at which angle i have to place the photodiode with respect to led so that i can receive the reflected light from the led

I would just put the LED(s) and detector(s) in separate black tubes as close together as possible, so that light from the LED(s) can't directly hit the detector(s).

Are you using three different coloured LEDs and a single detector or a white LED with three detectors, each with a different colour filter?

you will have to make sure you know the exact colour of the light so that the readings are not offset by it.