Glowing entities! This example file lights up blazes and magma slimes with their respective colors.

lights-entity.json

{
    "minecraft:magma_cube": [
        {
            "color": {
                "red": "rng(0.6) + 0.4",
                "green": "rng(0.1) + 0.3",
                "blue": "0",
                "alpha": "1"
            },
            "radius": "4 + 3 * flicker(5000)"
        }
    ],
    "minecraft:blaze": [
        {
            "color": {
                "red": "rng(0.2) + 0.8",
                "green": "rng(0.3) + 0.6",
                "blue": "0",
                "alpha": "1"
            },
            "radius": "6 + 4 * flicker(2000)"
        }
    ]
}

Please take in consideration the fact that this is very CPU intensive algorithm and thus it's a "little bit" laggy. Use with care.