We take extra care in verifying that the older Light Gray and Dark Gray are separate from the newer Light Bluish Gray ("blay") and Dark Bluish Gray ("dark blay"). We also make sure that Brown and Reddish Brown are separate. If you order items in these colors, rest assured you will not receive an item in the wrong color or we will refund, replace, or have the correct part sent to you.
Pinks and Purples are more difficult to distinguish and Lego Company's own consistency is historically poor in these hues. We do our best to list and describe the exact color of these parts, but if you have a concern, feel free to contact us before ordering. We have our own color chart of bricks in confirmed colors we can compare pieces to.
There are a few parts with a slight cosmetic difference that doesn't make the part functionally different.
The most common examples are:
There is not a way to mark that the presence of these differences is unknown. Sets come from the factory with a mix of each variation. In cases like these we try to to mention that the variation us unknown in each parts' listing. If you are looking for one specific variation, where the other version poses a problem for you, feel free to ask before ordering and we will check our inventory and let you know what we have in each variation.
Here is the Lego Color Chart We Use