I believe the STM is planning on abandoning the different coloured route depending on the type of bus.
While express buses used to be green, and on the map they’re displayed as magenta, the new bus stop signs on the West Island display the express bus as blue instead of green or magenta:
On Pie-IX, the express bus is also blue:
When I asked them about this, they said “We want to standardize the colours. We are reviewing the colours for the future and how to display these services.”
Because the standard ARTM signage displays the different bus companies by specific colours, adding more colours within those networks could be more confusing.