OK, further to what I was saying about colours (Pantones, CMYK mixes and RGB/Hex versions), I've had a play with it.
I've managed to find 2 Pantone colours that come as close as possible to the original colour mix taken from the current promotional material PDFs (the 'legalise Happy Birthday' etc posters), as they're presumably what people will be printing out so I've taken those colours as a basis.
Have also included my own suggestion for a colour, based on this original and it's ability to apply well across all printed/on-screen media with little change in the perceived tones. I found that a 30% mix of this solid colour worked well as a close match to the colour already in use on the promotional literature, so it gives use versatility to match existing work or use even lighter tones but also go darker up to it's solid (100% tint) version.
I've put all these into easy-to-use/view swatches which I've attached below. It Includes Pantone Matching System (PMS) references (particularly for those working in print design who have access to a swatch book), CMYK split, RGB split and the Hex value, so it's something everyone should be able to look at regardless of the software they have available and hopefully share their opinions.