On a Scigiene Salmonella plate, also known as a Salmonella-selective or enteric medium, the appearance of a purple color typically indicates the presence of certain Gram-negative bacteria that can ferment lactose. Salmonella itself does not ferment lactose, so it would usually result in colorless or colorless colonies on this type of selective medium.
However, if there are purple colonies, they might be due to other lactose-fermenting Enterobacteriaceae, such as Escherichia coli or other coliforms, which can produce acid and change the color of pH indicators in the medium. Make sure to conduct further tests to confirm the identity of the bacteria, as the color change can be indicative of other lactose fermenters rather than Salmonella itself.
To summarize, the purple color likely indicates the presence of lactose-fermenting bacteria, such as Escherichia coli, rather than Salmonella.