If you have a brown mid or high fire clay you like, then I would suggest wedging in some silica sand, if it is not already groggy, and trying a test. I usually use raku clay for its known raku qualities, but I also use other stoneware and occasionally porcelain bodies. I made some raku pigs and used a light brown firing cone 6 body. I knew that it fires pink in bisque, so when I raku fired it with a clear crackle got pink pigs. Same thing with using a red mid-range stoneware to take advantage of the bare clay getting very dark in the reduction to contract with a white crackle.
It is all about knowing what the clay body can stand while going up and pulling to open air. Some work fine, and others need help via addition of grog, or kyanite, wedged in. Knowing the red/brown body will get really black when bare and reduced, or another clay will give pink when bisque fired, or that a porcelain clay with molochite wedged in does fine, will open up your possibilities. Interest in raku indicates you are a curious person, so follow that curiosity and have fun while gaining knowledge.