If you are concerned about mold, do not go at it alone. Hire a mold remediation contractor to test the substance first.
If it is mold which is found to be harmful, you should move out until all of the remediation of the mold has been completed.
Since you are on a slab, you could have moisture present and depending on the interior humidity of the home these spots could be mildew instead.
My recommendation is to have your home properly tested as soon as possible to safeguard you and your family.
For more information:
Read "How do I know if I have mold in my house?" a Q&A answered by Sean Lintow.