many prefer to use a natural fabric such as cotton or silk and avoid any of the artificial fabrics such as nylon, rayon, or polyester.
Likewise your cloth can be made out of any color of fabric. Some will change their altar cloths with the seasons to reflect the changing of the Wheel of the Year. Or they may use a particular color associated with their Patron Deities. But there is no rule saying that you can’t just pick a color that speaks to you and use that.
Personally I would recommend using a material that you can throw into the washing machine when you spill wine on it or it gets smudged with ash from your incense. Nor would I use a very expensive piece of material because sooner or later you’ll either get candle wax on it you can’t get out or you’ll get holes in it from sparks from your candles or incense. You don’t want to be out a lot of money when you have to throw it away and make another.
Making a cloth isn’t hard. First measure the table you’ll be using for your altar. They you’ll need a piece of cloth that is a foot larger than the altar in order to have some drop of the cloth on each side. So if your table is 3 feet square you will need a piece of fabric that is 4×4 feet to cover it. You can then decorate the cloth in any way you like or you can leave it plain. That’s all up to you. You can use a cotton bed sheet you do not use any more and just cleanse it with sage or pine. Or you can go to your local fabric store and see if they have a yard of organic cotton material it would not cost more than five dollars and it can be any color for any feast or holiday. Then you can draw any type of designs that represent your gods or goddess’ and the occasion or make it one with a pentagram on it and use it for all rituals. Its all up to you!