There is no standardized rule or color code assigned to each chip as it will vary depending on the venue, region or preference. Furthermore it can vary within a venue, depending on the stakes.
However, the basic color schemes include red, white, black and green, but with new designs and manufactures coming in, additional colors have also been added such as pink, yellow, orange, grey etc. In order to avoid confusion, every chip will be assigned a dollar amount, in addition to being color coded.
All you need to do is to look at the color of the chip. Most casinos may use the same denominations as mentioned below, though it is not a universal rule to follow.
Red chips, also referred to as nickels, are worth dollar five.
Green chips, also referred to as quarters, are worth dollar 25.
Black chips are worth dollar 100.
Purple chips, also referred to as Barneys, are worth dollar 500
Orange chips, referred to as pumpkins, are worth dollar 1000.
Then there is the small matter of grey, blue or white chips, worth dollar one each.
In the United States, there are different variations. For instance, New Jersey and Illinois have uniform color patters. However, Nevada has certain exceptions. Red and green chips are consistent in most casinos nevertheless.