Fragrance oils are synthetically produced scents created to mimic smells - any smells, from flowers and herbs to fruit to perfume, and are usually petroleum based. Fragrance oils are not all-natural but are often listed as ingredients in all-natural soap. You might see an ingredient listed as, "rose oil," or, "mango fragrance," for instance, which implies that the ingredient comes from a plant source when it does not.
Bright, crayon looking colors should be a dead giveaway that something is not natural but brightly colored soaps, bath salts, and other bath and body are often marketed as all-natural. FD&C, food safe dyes, pigments, oxides, ultramarines, micas - none of them are natural. It's true that some may come from the earth but they undergo enough processing to disqualify them as natural.
And just to clarify, I don't think there's anything wrong with buying your favorite bright purple raspberry swirl soap - it really is a matter of taste. I just think that people have the right to know what they are spending their money on.
Here's a bullet point list from The Natural Ingredient Resource Center about what is or ain't considered natural:
NATURAL INGREDIENT CRITERIA
Natural Ingredients include
plant, animal, mineral or
present in or produced by nature.
produced using minimal physical processing.*
directly extracted using simple methods, simple chemical reactions or resulting from naturally occurring biological processes.*
Natural ingredients are...
grown, harvested, raised and processed in an ecological manner.
not produced synthetically.
free of all petrochemicals.
not extracted or processed using petrochemicals.
not extracted or processed using anything other than natural ingredients as solvents.
not exposed to irradiation.
not genetically engineered & do not contain GMOs (genetically modified organisms).
Natural ingredients do...
not contain synthetic ingredients.**
not contain artificial ingredients including colors or flavoring.
not contain synthetic chemical preservatives.