@rainbowR i would go through the help page for barplot until i got something i liked. specifically:

cols <- c("#e50000",
"#ff8d00",
"#ffee00",
"#008121",
"#1f3e8f",
"#742483")

barplot(rep(1, 6),
horiz = TRUE,
col = rev(cols),
space = 0,
border = NA,
axes = FALSE)