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The best way is to keep on looking! I gather that you can identify a woven carpet, and that's the important bit and I trust you can identify face fibre type. This will give you 90% of the information you need re. the likelihood of shrinkage and browning potential.
WILTONS
There are two basic types, whether plain or patterned. Traditional Wiltons will have the face yarn threads running in lines through the backing and will "break through" into the face of the carpet as and when required.
BELGIAN FRAME or Face to Face Wiltons are two carpets made in a single process. They can be plain eg Brinton's Bell Twist or patterned eg typical Belgian Wiltons. Think of a sandwich coming off the loom. The backings are on the outside and the face yarn on the inside. Knives slice through the face yarn, splitting the woven "sandwich" into two identical carpets. A patterned Belgian Frame Wilton will show it's pattern on the reverse, backing side, of the carpet. Obviously, a plain Belgian Frame Wilton has no pattern to show.
AXMINSTERS
There are two basic types of Axminster weaves. On both types, individual tufts are inserted and held held within the backing. Spool Axminsters are identified in a similar way to Belgian Frame Wiltons. The pattern is clearly visible from the backing. Theoretically, these could have as many different colours as your heart desired.
Gripper Axminsters are the most common manufactured today and tend to have, from memory, a maximum of twelve different colours as well as plain carpets. The pattern can be seen in the backing but it's not very clear because of the way the face yarns are "hidden" by the jute wefts.
My rule of thumb re. shrinkage with woven carpets is that if there are any weaknesses in the installation, an Axminster carpet MAY shrink and a Wilton carpet WILL shrink.
Safe and happy cleaning
The Ken