I've worked in broadcast & fashion/jewelry, together, and colors were a big part of it.
I thought 'chartreuse', naturally, but there are many versions and terms. If everybody is on the same page, and using the same palette and terms then it makes the collaboration successful.
The area in the red circle is close, but light does play a big part. But you can look up different examples of the colors. *
A close match for the top left ball may be something like a gold yellow, yellow pantone, etc.
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*
http://en.wikipedia.org/wiki/Shades_of_yellow
http://en.wikipedia.org/wiki/Chartreuse_(color)
(edit: I agree Andyson with your "Really no need to specify a RGB or reference a color chart IMO. If they produce it using their existing Srixon neon yellow I'm good with that. Keep it simple."
New chant:
'We want Srixon neon yellow Callys!!"