/usr/libexec/rainbow/backend.sh: line 46: 096: value too great for base (error token is "096")

After upgrade to TOS6:

$ rainbow brightness 3
$ rainbow indicator-1 255,0,0 enable
/usr/libexec/rainbow/backend.sh: line 46: 096: value too great for base (error token is "096")

This is because uci -q get rainbow.all.brightness outputs zero-prefixed values which are interpreted as octal numbers by shell. 096 is not a valid number. Similar issue exists for other brightness levels (although they don't result in an error message, just incorrect computation).

$ for i in $(seq 0 8); do echo -n "$i: "; rainbow brightness $i; uci -q get rainbow.all.brightness; done
0: 000
1: 032
2: 064
3: 096
4: 128
5: 160
6: 192
7: 224
8: 256