First thing to get straight, mate: RAL isn't a paint you pop into a tin at the merchant. It's a German colour-matching standard — a numbered system of around 207 shades in FiniSpec — that paint and powder-coaters mix to so a colour comes out identical every single time, in any factory, anywhere in the world. That's the whole point of it.
Where RAL earns its keep is anything industrial, architectural or metal. Steel doors, gates, railings, radiators, plant machinery, fleet vehicles, fascias and signage are nearly always specified in a RAL number. If an architect or fabricator hands you a spec sheet, the colour will be RAL — say RAL 9005 Jet Black or RAL 7016 Anthracite Grey for those modern dark window frames everyone's after. Powder-coated aluminium windows live and die by RAL.
The palette reflects that job. The strongest families are greys (36), greens (33), browns (24) and blues (22) — practical, hard-wearing, no-nonsense colours. The full range runs from a near-black LRV of 0.3 right up to a bright 97.2, so there's plenty to work with for exterior steel and cladding. The blues are genuinely lovely if you want a bolder accent: RAL::Azure blue, RAL::Green blue and the softer RAL::Light blue all read clean and confident on metal.
Now the honest caveat. RAL is not what you want for living room walls. The colours are flat, engineered references — they lack the pigment depth and the way-it-shifts-with-the-light magic that decorative brands build in. For interiors you'll be far happier with Farrow & Ball, Little Greene or Mylands.
Practical advice: if you've a steel door, railing or radiator to match, get the RAL number from the fabricator, then have your decorator's paint tinted to it in a proper metal-grade system — Hammerite or Rust-Oleum for direct-to-metal work. Match the number, not your memory of it.