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The problem is that your salt stars are being formed only after some of the "unsalted" dye has already reacted with the fabric. After that, the extra dye involved in the stars does not show up much.

Unlike wool dyes, reactive dyes do not exhaust on cotton. Exhausting is when all of the dye leaves the liquid and sticks right onto the wool. Fiber reactive dyes always leave a whole bunch unreacted, or else already reacted with water and unable to react with the fiber, so it always looks like you wash a lot of the dye out. What you see on the fabric before washing does not tell you what you will see on the fabric after washing, because some of that dye is not attached to the fabric and must wash out. You have to have MORE dye on the fabric than you want to end up with! It should look way too dark, before washing.

You should have your fabric stretched out. Having the fabric stretched tightly makes the salt effects form much better than if it is lying loose in a pile. You can pin the fabric to a frame (I like the wooden stretcher bars that painters use to make frames to stretch their canvases over to make oil paintings), or you can just try to spread it out well on a sheet of plastic.

Now, working quickly, apply the dye and IMMEDIATELY throw on your big crystals of salt. Don't give the dye any time to react with the fabric before you toss that salt on! You may have to apply dye to just one part of your fabric at a time, throw the salt onto that section, then go on to the next. You don't want to give the dye time to react with the fabric before the salt crystals get on there. You have to hurry if the soda ash is already in the fabric, by the usual tie-dyer's presoak in soda ash solution, because cotton + dye + soda ash = immediate reaction.

It would not be a bad idea at all to temporarily reduce the temperature of your dye reaction. If you had access to a refrigerated room, as in research labs, you could do the whole thing in there, then bring the results out into the warmth to react. What you might really do is refrigerate your dyes, and use them straight out of the refrigerator, so they react well only as they warm up. Cold reactive dye does not react well at all. This is just an idea. Applying your soda ash after the dye, instead of before it, is another approach that will make a big difference.

The normal way to apply the all-important soda ash, for a tie-dye kit, is to presoak your fabric in soda ash, then squeeze it out and either use it wet, or line-dry it before applying the dye. As soon as the fabric dye and soda ash all combine, the reaction begins. The reaction is fastest for fuchsia (red MX-8B) and slowest for turquoise (turquoise MX-G). You don't have to do it this way, though. You can also mix the soda ash in with the dye (which means it only lasts about an hour in the bottles), or you can even after-soak your fabric with the high pH, after the dye is on the fabric. This last might be a good way to maximize your salt effects. You can paint on sodium silicate solution, as a substitute for soda ash (Dharma sells this as After-Fix, and ProChem as PRO Fix LHF), or you can dip the fabric in a solution containing salt (to keep the dye from dissolving in it much) plus soda ash. Dissolve enough salt in water that not all of it can dissolve and some is left at the bottom even after stirring; this is called a saturated solution of salt. That's 2.4 pounds of salt per gallon [4 liters] - use a little extra to be on the safe side. Also add soda ash to the salt solution, one cup [250 ml] of soda ash per gallon of water. Mix thoroughly; soda ash dissolves most easily at about 95°F (35°C). Allow your fabric to dry, with more dye visible on it then your really want since it always washes out lighter - it should be really dark - then dip it in this solution, enough to get it quite wet, then spread it out or wrap it in plastic, and keep it moist for 24 hours or so.

Don't waste money on expensive tiny jars of "silk salt", you can get the same thing for a small fraction of the price by buying a big bag of rock salt for deicing sidewalks or for making ice cream, or a box of kosher salt for a somewhat smaller size grain. Of course you can use any kind of salt, even the tiny-grained table salt, to make your saturated salt solution. Most dyers use non-iodized salt, as some dyers claim that iodized salt causes streakiness in the dyed fabric.

Also, don't waste much more money on those tie-dye kits. They are a GREAT way to get started, but they are rather expensive, since there is so little dye in each kit. You need to start mail-ordering your dye. You can buy little 2/3 ounce jars of Procion MX type dye from Jacquard at some of the better crafts stores, or even from Amazon, for about $3 to $4 per jar, or you can more economically order bigger 2-ounce jars from PRO Chemical & Dye for about $5 each. Even with the high cost of shipping, the bulk costs for two-ounce and larger jars save you a ton of money! See my page of links to Sources for Dye Supplies Around the World for a lot of different dye suppliers you can order from. Order your urea along with your dye, but get your soda ash in five pound jugs of "pH Up" or "pH Increaser" at the hardware or pool supply store - make sure the label says "sodium carbonate".