The Crafting system has 5 quality types:
1. White
2. Green
3. Blue
4. Purple
5. Yellow/Gold
In order to get a 100% chance of getting any desired quality/color, you need to use the same material and item quality.
To have a 100% chance of getting a gold item, you would need to use only gold materials and gold items.
If you select 5 gold materials and 1 purple (meaning that you are using an item that is one quality level lower), you would have a 50/50 chance of getting purple or gold.
If you select 5 gold materials and 1 blue (meaning that you are using an item that is two quality levels lower), you would have about a 45% chance for gold, a 12% chance for purple, and a 42% chance for blue.