Tone of a voice includes aspects like timbre (the natural unique sound every voice has), depth - which can be shaped, the positioning of the singing voice (i.e. where it is coming out from). it is a lot of abstract concepts until you figure it out or if a singing instructor guides you. For example, most untrained people sound very 'shallow' when they sing because they don't know how to add depth, some sound very nasal because they learnt to speak like that when they were young and so on..
In your case, your tone sounds slack and juvenile (note that these are not terms to discourage you!) because you still lack a lot of muscle activation required to sing in a nice sound. I was like that too when I first started singing =)
Blessed,
Gary.
