If you are using an editor that can do layers, your alpha mask file can be created as a layer, then merged. Then you no longer need to include an alpha file. You can even do the alpha effect with line and shape tools by setting the alpha value for the color of your nimbus effect very low. When it overlays on your primary color lines for the reticle structure, it will change them also. So you may need to start with a color value for the rings and lines that the alpha brush effect will also bring up to the finished color you want.
The reticle was projected visa a lens porthole and often that was noticeable as a large diffused color spot that the reticle projection sat in the center of. This was due to the light diffuser placed between the bulb and the reticle insert. Japanese gunsights for daytime operations projected a white reticle. The historical mistake for all air combat games is thinking the pinkish orange reticle was the daytime reticle. That is simply the night time diffuser engaged.
For daytime operations in ww2 the reticles were white or yellowish depending on the color of the daytime diffuser. The intensity of the color was controlled by the dimmer. The Germans used blue, green and red diffuser for nighttime, while daytime was white or slightly yellowish. The British night reticle had a blanking plate that reduced the ring and dot to three horizontal dots of yellowish orange. Optical gunsights for turrets often had red or orange diffusers like the MKIII\Mk9 in the Lanc, Mossi6, and M16.
A very common problem with gunsights was glare on the reflector plate and the windscreen which impacted aiming with double images or obscuring ground targets. That is why the AAF K14 family projected only a white light reticle from the factory for the fixed and movable 6-star. A common complaint about the K14 reticle was it disappearing while aiming at a con flying near white clouds. The 6-star points were small diamonds not elongated blobs due to the span and range wheels that made up the reticle plate.
Not very sexy in 21st century shootem up games. The reality for a ww2 pilot was that he only wanted to see just enough of that reticle to help him aim, not blitz his eyesight with neon pizazz, or block his field of view. Another common mistake in air combat games, the Japanese Type98 and Type4 are both 135\140 Mil in diameter reflecting the slow velocity of their cannons from what I've been able to determine.
