Generally, a newsletter is meant to do two tasks: informing people about something or persuading them to do something. For example, a newsletter may inform your clients about your new product or inform them to check out the company's website for the latest information.
When you are writing your proposal, attention to detail is very important. You must write everything in clear and concise English. You should never use slang and only use the technical terms that you must use. The person who is reading your proposal may be a lay person and become confused if you use too many technical terms or job related slang words and phrases. Color for your graphs and charts is quite acceptable and as it eye catching can mean the difference between submitting a wining proposal and one that ended up in the "also ran" file.