Is it tradeable? And how much spice to add to get 2+ in a random skill?

no and it is random

Red Spice affects: Attack, Strength, Defence, Ranged and Magic

 

 

 

Orange Spice affects: Smithing, Crafting, Fletching, Runecrafting, Cooking and Construction

 

 

 

Yellow Spice affects: Prayer, Agility, Slayer and Thieving

 

 

 

Brown Spice affects: Woodcutting, Herblore, Farming, Fishing, Mining and Firemaking

 

 

 

 

How it works

 

 

 

You can only use a maximum of 3 doses of a colour in a stew, and the colours/doses will determine what the stew will do.

 

To work out how the stew may effect you, you need to get the number of doses you put in, and multiply it by 2. This is the maximum you will gain or lose, please note that it is up to this number. For example, if the number is 6 you may get 4.

 

 

 

Of course, this means if you are lucky, you could temporarily boost any of the skills mentioned above by 6! (Or, if you are unlucky, temporarily lower the skill by 6.)

 

 

 

If you want an extremely variable stew, try putting 3 doses of each colour in and see what happens!