You need to enhance your vocal harmonics to make your voice much richer...
Well this is one of my favourite subjects. You often hear people talk about 'harmonics' but what are they really? In fact, in case you didn't know, they are the same thing as overtones. Before I explain what they are, I'll give you my 'picture' of what they are: In a way, Harmonics are to a musical note what the colours of the rainbow are to white light.
At the same time as you hear any given note, many other notes are sounding, (like the rainbow colours) -although less strongly than the main note (which is like the white light)....., and those notes are always in a certain pattern, or relationship, to the main note.
We hear these overtones, (they are called this because they are higher than the main note) in every musical sound we ever hear. - whether that is a sung tone, or a note on a piano, or a wooden spoon tapped on the side of a saucepan. They are like the fabric of vibration.
The really useful thing to know here is that when you sing, those harmonics are already there in your voice, but the way you use your mouth and body can either bring out the overtones, making your voice sound more 'colourful' or 'richer', or can damp down the overtones making the sound duller and less engaging to people's ears.
There are 15 overtones sounding above every main note and they occur in the pattern shown. Where '1' is the note that you officially call it, e.g, C.

( I'd like to point out here that the reason that we can understand language is that every vowel we speak emphasises different harmonics, i.e they have specific patterns that enable our ears to distinguish them from each other. Amazing hey?)
Anyway, 'How do I enhance the overtones for a richer voice?' I hear you ask. Well, the answer is that you need to enlarge the resonating space inside your mouth!
There are three key ways to do this:
1. Smile when you sing! This lifts the soft palate
2. Widen your throat.
3. Lower your larynx.
Each of these actions makes a huge difference to how rich, warm, bright, colourful, and ringing your voice is. You can do them each separately for distinct qualities, or all together for a very rich and powerful sound.
So to sum up, Harmonics create a variety of 'colours' in your tone or timbre, which gives you a richer and more variable sound. You don't get stuck in 'one way' of singing. When you learn how to do this and gain proper control over it, you will have greater expressivness, versatility, creativity and power in your voice. And it helps with your projection too.
It's all about knowing how to exploit what you've already got within you. Being able to milk your innate resonance. Because most people simply do not make the most of their natural resonating ability.
... it's a case here of 'what you don't know, could really help you'!
If you're keen to fully discover and tap into your inherent resonating capacity for richer more powerful singing, then I highly recommend you check out my mini-course, 'Reclaim Your Rich Resonance'.
It really is one of the most fun and fulfilling areas of the voice to explore! It opens incredible new doors in your singing.