[p3lim]

As lightspark suggested, use the ClassPower element and add this PostUpdate callback:

local function PostUpdateClassPower(element, cur, max, hasMaxChanged, powerType)
    if(powerType == 'SOUL_SHARDS') then
        for i = 1, max do
            if(i <= cur) then
                -- purple
            else
                -- green
            end
        end
    end
end