I need to customise the colour code for protein multiple sequence alignment (MSA), However the existing R packages only supports the predefined colour codes, which are single letter based. But, I have to assign my own colour scheme for a pair of letters (amino acid). I have gone through the packages like ggmsa and ggplot2 etc., but failed to find the solution. I need to generate a figure as shown below,

I tried with the following scripts but failed to complete my task.

library(tidyverse)
library(ggtree) 
library(seqinr)
tree = read.tree("tree.newick") 
msaplot(p=ggtree(tree), fasta = "msa.fasta")
msaplot(p=ggtree(tree) + geom_tiplab(align=TRUE), fasta = "msa.fasta")