Dye lot variations are slight differences in color between production runs of the same style of item. Dye lots are batches of textiles or fibers that are dyed in the same vat at the same time. No two batches of yarn are exactly the same. Even lots that are done right after the other will have slight differences in the  final color. Yarn is much the same way.  If the yarn base is different (from a different sheep, processed slightly differently) you will get different color results even in the same dyeing process.

We will strictly control every link in the production process to reduce dye lot variations. To ensure a consistent color in a finished drapery, the factory will try best to use yarn that comes from the same dye lot.
We will make sure that the fabrics for an order are from the same batch to ensure that the same order is delivered to the customer with as little variation as possible.
We will strictly match the color of the fabric according to the color card to reduce the color difference with the original fabric color.

Try ordering drapery that "work together" in one order.  For example, the curtains for a window should be in an order.
In order to avoid Dye Lot Variations under different lights after you receive the products. Be sure to use D65 or daylight near noon to check the color.
*D65 is a CIE standard illuminant that represents a daylight color temperature of 6,500 degrees Kelvin. This corresponds to daylight near noon. D65 is the most commonly used daylight illuminant.