Ravenclaw colours

[Pippin]

It looks like (from official WB products) movie!Ravenclaw colours are 
(dark) blue and grey, while canon!Ravenclaw house colours are blue and 
bronze (whatever 'bronze' means as a single colour, I have not 
determined). Do you have knowledge or a guess as to why there is a 
difference? Perhaps they could not reach consensus on 
fabric/yarn 'bronze' and found grey or 'silver' easier to portray on 
screen?

I am confused by 'bronze', because the bronze I have seen ranges from 
copper (rose/pink-brown) to very dark brown. Yet in my informal 
survey, people tend to point at brass/gold things when I ask them to 
point at something that's bronze.

Pippin Fowler
wishing JKR and the movie makers had chosen heraldry colours instead:
Or (gold/yellow), Argent (silver/white), Azure (blue), Gules (red), 
Sable (black), Vert (green), and Purpure (purple)