Font colours changing

Hi all,

Hoping someone may be able to help me! I have a project that I am translating for a client. This client has very specific colour schemes that we must stick to. For some reason, when I open the file from the client, the colours change and when I send the file back to the client to review, the colours have changed for them as well. Any ideas how I can stop this happening/solve this?

When I look at the slides in the general story view, the colours appear to be OK, but when I go into the individual slide view, the colours are darker.

Any ideas would be greatly appreciated!