The older the individual, the darker the colour will be. Looking at the photographs of this grass bug on Bug guide I'd say this was a younger one. It was about 5-6 mm long and came in to a sheet that we had a light focused on for attracting moths. It was so small that there was no way we could see the beautiful colours until the photograph was taken!
Every, D., J.A. Farrell and M.W. Stufkens. 1992. Bug damage in New Zealand wheat grain: the role of various heteropterous insects. NZ J of Hort and Crop Sci. 50. 305-312.