All information I wrote below is not case for spruce leaves bcs they don't change like other leaves when colormap applied (with birch). Still would recommend to check in java. Maybe in your case if you'll change texture (colourless) you would get same results. Or change block model 🤷🏼‍♂️. Or still make colorless textures?

Well, not much helper in here, but apparently you should create black and white texture and in wiki or www.reddit.com/r/Minecraft/s/0h1wWVUj2E you may found something useful