Chemical stains and dyes produce a unique look to each concrete floor to which they are applied.
This uniqueness is a benefit and a large part of the attraction to concrete floors. That said, it is vital to produce a sample of what the floor will look like after it is stained and sealed. There are so many factors that affect how the chemical stains react with the concrete - quantity of cement in the mix, the age of the concrete and concrete finishing methods, to name just a few - that a sample must be made on the actual floor you are going to be staining.
Certainly, your website and portfolio can attract a prospective client, but that is no guarantee you can match identical colors since every load of concrete is different. Most manufacturers of chemical stains or dyes provide color charts displaying their colors. Review color charts and color chips with the client. Keep in mind that color charts are photos of the color that have been laminated onto paper and not actual concrete. Color chips and color charts are simply starting points.