Plot letter strings in ggplot2 plot

I have a following dataframe:

readname <- c("tic", "tac", "toe")
sequence <- c("TTTTTTTTATTTTTA","TTTTCTTTTTTTTT","GTTTTTTT")

df <- data.frame(readname, sequence)

and I want to plot it using ggplot2, so the y axis would contain "readname" column and the strings stored in column "sequence" would be plotted horizontally, one below the other, all aligned to right. I would also like to assign color to every letter (e.g. A - red, T - blue, C - green, G - yellow).

I tried to use geom_text() but I produce either empty plots or plot every string on the same level (collapsed) or plotted on the various levels, unaligned. The same applies to geom_label().

One of my attempts:

ggplot2::ggplot(df, aes(x=sequence, y=readname)) + ggplot2::geom_label(label=sequence)

Here is something I would like to achieve (from text editor):

library(tidyr)
library(dplyr)
library(ggplot2)

df |> mutate(letters = lapply(strsplit(sequence, split = ""), rev)) |>
  unnest(letters) |>
  mutate(pos = row_number(), .by = c(readname, sequence)) |>
  ggplot(aes(x = max(pos) - pos, y = readname, color = letters, label = letters)) +
  geom_text() +
  scale_color_manual(guide = "none", values = c("red3", "green4", "orange", "blue")) + 
  scale_y_discrete(limits = rev(readname)) +
  theme_minimal() +
  theme(
    panel.grid = element_blank(),
    axis.text.x = element_blank(),
    axis.title = element_blank()
  )