Is this what you want to do?
library(tidyverse)
# Sample data in a copy/paste friendly format, replace this with your own data frame
flies <- tibble::tribble(
~Ophaling, ~Boomtype, ~Bestand_nummer, ~Val_nummer, ~Kleur, ~Kolom1, ~Grote_vliegen, ~Kleine_vliegen, ~opmerkingen,
1L, "B", 2L, 1L, "B", NA, 2L, 6L, NA,
1L, "B", 2L, 1L, "W", NA, 6L, 3L, NA,
1L, "B", 2L, 1L, "Y", NA, 7L, 6L, NA,
1L, "B", 2L, 2L, "B", NA, 3L, 2L, NA,
1L, "B", 2L, 2L, "W", NA, 8L, 7L, NA,
1L, "B", 2L, 2L, "Y", NA, 5L, 15L, NA,
1L, "B", 3L, 1L, "B", NA, 4L, 14L, NA,
1L, "B", 3L, 1L, "W", NA, 15L, 29L, NA,
1L, "B", 3L, 1L, "Y", NA, 12L, 15L, NA,
1L, "B", 3L, 2L, "B", NA, 34L, 43L, NA,
1L, "B", 3L, 2L, "W", NA, 168L, 47L, NA,
1L, "B", 3L, 2L, "Y", NA, 52L, 32L, NA,
1L, "B", 4L, 1L, "B", NA, 2L, 2L, NA,
1L, "B", 4L, 1L, "W", NA, 17L, 7L, NA,
1L, "B", 4L, 1L, "Y", NA, 46L, 6L, NA,
1L, "B", 4L, 2L, "B", NA, 2L, 5L, NA,
1L, "B", 4L, 2L, "W", NA, 12L, 4L, NA,
1L, "B", 4L, 2L, "Y", NA, 24L, 14L, NA
)
# Relevant code
flies %>%
group_by(Kleur) %>%
summarise(Aantal = sum(Grote_vliegen)) %>%
ggplot(aes(x = Kleur, y = Aantal, fill = Kleur)) +
geom_col(alpha = 0.7) +
theme_bw(base_size = 12)

Created on 2021-12-27 by the reprex package (v2.0.1)