I never advise on colour, APG. Materials, yes, but as i said earlier, the homeowner is the one who has to live with the colour scheme. And i have been called back on a few occasions because the customer has decided that they actually don't like the colours they have chosen.
As for testing different shades/colours before settling on the required scheme, please, postman, do not do what lots and lots (and even more lots) of people do. That is to lay the paint on as thick as they can. Remember that your decorator will most likely use a roller to apply the paint and a roller distributes the paint thinner than a brush. Even were he/she to use a brush, he/she would not apply as thick a coat as the person doing the testing, and the areas tested will be difficult to cover. Far better to use a few sheets of blank paper and pin them to the wall.
Hope that makes sense :-/