In my company the wireframes are supposed to be in gray-scale because the visual designer takes care of the visuals aspect. For my side project, I wish to add colors to my wireframes. It would be really great if I can have some resources which is really useful and best practice in the industry.
As Michael Lai has said, and let me take it one further...
Blueprints and Wireframes are so named because their entire purpose is to remove connotations of values, weightings, qualities and attributes non-essential to understanding the whole, as a whole, whilst giving balanced, equal importance to each and every detail.
Kind of like the promise and potential of communism.
But instead of red, go with shades of blue, hinting at... blueprints:
Ask your colleagues in the visual design department
If you have a decent relationship with your colleagues at work who do the visual design, they would be the ideal place to start (assuming your workplace is not hostile to sideline projects).
The designers that you dove-tail with are the ones who best know how to take your usual deliverable (wireframes) and take it to the next step. Other organizations, or resources on the web, will generally not do things exactly as your organization does.
Most folks are happy to talk about what they do for a living. Let a designer or two that you respect there know of your plans, and tell them you’d be interested in hearing their opinions, maybe over lunch.
Just make sure your boss would be OK with it
The caveat is, you want to be sure there is no possibility this will reflect badly on you in your company. Most employers are smart enough not to forbid their technical workers from getting valuable experience in their free time, but some places don’t understand this.
It's not what your company or colleagues want. If it is your job, and it sounds like it is, to liaise with customers to find out their requirements and create initial wire-frames, then the detail that you include in your wire-frames will be driven by the customer.
Your designer should be less precious and always remember that wire-frames that are produced at this stage will always be low-fidelity and they will produce the high definition frames.
There's an advantage to this that your designer and possibly your boss hasn't realised. The more information you can glean up front and include in your wire-frames, the less work the designer has to do to ensure they get the design right and it has a better chance of being right as you are all better informed.