How do I use a custom colormap for my grass and leaf blocks?

Hi

 

Not sure what you want but these from BlockGrass might help

Block:: 
    @SideOnly(Side.CLIENT)
    public int getBlockColor()
    {
        return ColorizerGrass.getGrassColor(0.5D, 1.0D);
    }

    @SideOnly(Side.CLIENT)
    public int getRenderColor(IBlockState state)
    {
        return this.getBlockColor();
    }

    @SideOnly(Side.CLIENT)
    public int colorMultiplier(IBlockAccess worldIn, BlockPos pos, int renderPass)
    {
        return BiomeColorHelper.getGrassColorAtPos(worldIn, pos);
    }

-TGG

Just FYI, if you plan on using biome data (temperature and rainfall), make sure to clamp the values so you don't cause array index bounds errors when another mod modified those values (say...by making the nether hotter than a desert, etc)