To change the transparency , you would put the first value of 255 which is (A) , also known as Alpha. The Alpha is the opaque.
To make it fully transparent and see through , you would put (A) to 0. To make it not see through at all , you would put the value to 255.
To make it transparent black , i would set (A) to 100.
Code:D3DCOLOR_ARGB(255,0,0,0)