[msk-lywenn]

I doubt it required floating point rgb and, iirc, it came (for real) much later. GPUs used fixed point math behind the scenes for a long time. The only thing you need to get proper additive blending is saturation, so that you don't overflow, like on the N64.

[lightingthedark]

You don't need floating point RGB for additive blending, but to get correct behavior when using additive blending for your light sources, you must use linear buffers and if you do that, the dynamic range of the scene won't fit in eight bits.