I would suggest this:
Candida sis absitque invidia (for a female)
Candidus sis absitque invidia (for a male)
This means "may you be white and may malice be gone".
I only chose one possible translation of candidus to keep it simple.
All the meanings are included, of course.
You wanted to have the element absit invidia.
As pointed out in a comment, it is a wish "may malice be gone", not "without malice" or "absence of malice".
These three things are semantically very similar, but the grammatical difference is huge.
Because this last part is a wish, it makes sense to make the beginning a wish, too.
I used the verb sis ("may you be").
I thought it would be appropriate that you wish the person to be candidus.
The use of second person also makes this more personal.
The gender of the adjective must match the gender of the person.
Therefore there are separate versions for a female and a male recipient.
If you want it to be "may I be" instead of "may you be" — which might make sense if others are supposed to see the text around the wearer's neck — then you should replace sis with sim.
In "dual expressions" like this one a chiastic word order often works best.
I put the two verbs sis and absit next to each other.
This also emphasizes the difference between the underlying verbs esse ("to be") and abesse ("to be away").
For some reason -que sounds good to me in this use, perhaps because it seems to tie the two statements closer together.
You can replace absitque with et absit if you want.
On your suggestions:
The gender of the adjective must agree with that of the corresponding noun, so a "white heart" would be cor candidum, not cor candida.
The adjective is often put after the noun, but the word order is free.
Whether or not you have cor, the phrase sounds weird.
Candida et absit invidia is roughly "white and may malice be gone".
The role of candida is unclear.
That is why I suggested adding sis/sim to make it into a two-part wish.
I would therefore say that your suggestions are not correct.
I prefer not to discuss whether something sounds good before it makes any sense.
The things I used to make my suggestion sonorous were chiastic word order and the opposing verbs esse and abesse next to each other.