Match your natural hair colour to one of these swatches. This is what we call your base number.
With Oiamiga you can lighten natural hair by one shade (or two shades if you're lucky). So, if your base number is 5, the lightest colour you can choose is one that starts with a 6 (or 7 at a push). And you can choose any colour darker than your base number.
But remember, if you've got previously coloured hair you can only choose an Oiamiga colour that's the same base number or darker than your coloured bits.