Astro....
If you are new to this, stay with the X2 for doing your basic colors. If you have an eye for color and like to play with customizing colors, then it may pay you to mix vendors to purchase small bottles that use can use to tweak colors. The smaller bottles found elsewhere are weaker by comparison but X2 is so strong that using it in tiny amounts can often be too much. Until you get a real handle on this plastic and color play, stick with the X2.
Remember to keep a note pad and to create a recipe book of your own. Write down every last detail and addition for each color you make so you have a specific reference to go back to.