No it's not really like a red day.
To have a true SP day, you can't have any pasta, rice, potatoes, fat free yogurt/fromage frais or any other 'free' food. There is no way to syn free foods, and you can't use synned alternatives to free foods (i.e. the McCain jakcets are 1 syn each, but still wouldn't be 'acceptable' on a SP day)
Which books are you looking at mummybear? Do your books have the Speed and Protein foods in them, or do yours show Super Speed foods?
If you need a list of what the speed and protein foods are, google 'slimming world list of s and p foods' there's a lovely list of these on Pintrest too. (It's a really long list for me to sit and type!)
You basically choose from those - half a plate of speed foods, and half a plate of protein foods (it has to be half and half for it to work properly)
You still get your 5-15 syns each day, and your healthy extra choices, but you get a second hex b choice (bread/cereal/etc.)
Does that makes sense???