The tl;dr version: The more information you give me about what you want, the less time it takes me to create it. The less time I need to work on creating a design, the less likely I’ll need to charge a fee for that time.
I generally don’t charge for the time it takes to create a design, unless it’s a very complicated design or a lot of revisions are necessary. In order to avoid the latter, the customer should 1) know what they actually want, and 2) let me know what they actually want.
A vague description such as, ‘I want an old-style floral pattern, and I want it to be kinda small, in yellow and lavender’ is better than no information at all, but I need to know what yellow and lavender, and I need to know what ‘kinda small’ means in this context. Also, all my floral patterns are “old-style,” since I specialize in reproductions of medieval/Renaissance designs. What era are we talking, here, and what culture? Byzantine? Fifteenth-century Spanish? (‘Kinda small’ for a Renaissance damask could be a 12-inch horizontal repeat, if the original textile was twice that size.)
Also concerning color… I cannot work from Pantone colors; please do not send me a Pantone code and ask me to duplicate that color. I can work from a hex code (example: #8e0800, which is a lovely red), and if you have the hex codes for the colors you want, that really simplifies things.
If the customer doesn’t need an exact match – if all they need is ‘red and yellow/gold that look good together and aren’t too saturated’ – I can work from that, too. If they want, ‘THIS design [includes name of design and/or link to it in my online shop], but half-sized and in the blue from your “Renaissance Damask with Cats – Prussian Blue” because that’s my cat’s favorite color,’ the whole process of creating a design to those specifications would take less than an hour, and probably not require any revisions after I send the initial test image to the customer for approval.
(If the customer does need an exact match, they’ll need to purchase a test swatch of the design printed on the fabric of their choice. You cannot go by what the colors look like on your computer screen. Even many greys print lighter or darker than they appear onscreen.)
Unless I am specifically asked to do otherwise, all custom heraldic designs will be made using same colors I use for my other heraldic designs. (See any of my SCA/”Creatively Anachronistic” collections for examples.) This is because these colors look good together, have good contrast (the whole point of having rules about what colors can go next to each other in heraldry), and are strong without looking harsh. (I’ve noticed that many designers who do SCAdian stuff seem to use the same hex codes as are used for electronic submissions of heraldic devices… Thus, the yellow is intensely lemony instead of golden, the green is eye-searingly bright, the purple is too blue, and the blue is too dark.)
So that’s color. Another consideration is size/proportion.
Say a customer wants an allover heraldic ermine pattern. The color isn’t in question; ermine is black on white. But what size for those ermine spots? How far apart, or does that matter? (Also, should they be fairly simple, or should they be those extra-fancy ones with the spikey ends?)
There’s no way to cover every possible eventuality here, but you get the idea: the more information I have upfront, the more smoothly the design creation process works for both me and the customer.