We mix a range of colours in vernites waterbased paints, for interior or exterior use, using a standard RAL colour chart as a reference.
When using a RAL colour chart, or any other colour chart, it is very important that your sales force and your customers are made aware of how this process works, and what the role of the colour chart is.
The following points must be borne in mind, and everyone concerned informed of them:

1: A colour chart is to be used as an initial guide only, a starting point to decide between types of colour, or ranges of colour.

2: The paint actually mixed according to a colour card formula will seldom exactly match the colour card version when it has been applied to the job. Sometimes the difference is quite marked, as application methods and substrates vary a lot. For example, paint that is sprayed appears a different colour to when it is brushed or rolled; paint applied to plain MDF can appear a different colour to the same paint applied to solid wood.
These factors, as well as lighting conditions, thickness of coat, sheen level, grain texture, sanding, and number of coats; will all change how the colour appears to the eye.
Wet paint in the can never matches a colour card.

3: Colour cards should be avoided when discussing colours with clients: they will lead to disagreements. It is best to show actual painted samples instead. If a colour card must be used in this way it must be made clear to clients that the finished article will not match the colour card exactly, for reasons mentioned above.

4: When agreeing a colour with a client, the user must apply the paint to a sample of the material to be used in the job, using the methods that will be used. This sample should be the colour discussed, and the colour card should be ignored for this purpose. The important thing is whether the client is happy with the colour arrived at through our mixing and the user's application. This colour is the true colour in reality. The card is merely a representation of what the colour looks like printed on white paper.

5: We will do our best to ensure consistency of colours between orders, and will work with our customers to resolve any issues.