[R] Adding overlap legend to a histogram

[Ogbos Okike]

Dear Experts,
Greetings.

I am trying to display two datasets in a histogram. I have been able to
plot the graph and added the legend for the two colors. I am, however,
having difficulties adding a legend to represent the regions of overlap
(the third legend).  Below are my data and code.

Thank you very much for your kind response.
Best wishes
Ogbos


Part of the two data are:
96 11 28 -5.0439243156971
96 11 30 -6.47673663925309
96 12 03 -6.82839470197342
96 12 05 -6.21642465505491
96 12 07 -6.25580747537018
96 12 10 -5.77540853474434
96 12 14 -3.98857218877879
96 12 16 -4.25191042337454
96 12 20 -3.20551034549018
96 12 24 -4.2702754047348
96 12 28 -6.03085851418479
96 12 31 -6.51403505358144
97 01 02 -6.32673280540791
97 01 08 -5.8537576420137
97 01 13 -5.54092007919419
97 01 23 -4.03617528404112
97 01 28 -6.21414660666954
97 01 30 -5.82248535055029
97 02 02 -4.52703090771556
97 02 04 -4.24731404905759
97 02 06 -5.22553031464346
97 02 10 -3.31737825603324
97 02 13 -1.48147648915881
97 02 16 -1.80195032791485
97 02 19 -2.16701154625054
97 02 21 -2.06571846213066
97 02 24 -3.39623775344558
97 03 02 -4.70829707054833
97 03 07 -3.73377684116639
97 03 11 -2.76476446486583
97 03 19 -2.30766786606313
97 03 21 -2.36150976836853
97 03 24 -1.84664525535518
97 04 01 -4.30618772775492
97 04 12 -4.51646004530582
97 04 19 -4.12507873323636
97 04 23 -3.46413598467606
97 04 25 -2.95371560706153
97 05 02 -4.04170720343953
97 05 13 -5.60975985858423
97 05 15 -5.52471869367602
97 05 23 -3.85761006637094
97 05 26 -3.47054347969788
97 05 29 -3.46506967197854
97 06 04 -0.307928317047413
97 06 08 -2.87534017937205
97 06 11 -3.00325467983916
97 06 14 -3.15331224991201
97 06 26 -3.14375164434693
97 07 02 -1.28362211606

and the second is:
98 05 02 -4.09334391050803
98 06 07 -0.161822520097844
98 06 19 -0.274151702680992
98 06 21 -0.285384620939307
98 06 25 -0.554974659138863
98 08 23 -2.22867947962777
98 08 27 -5.44129410150581
98 09 25 -4.46403021303242
98 11 09 -0.723468433013585
98 12 14 -0.824564697338419
99 01 16 -0.880729288629993
99 01 19 -0.566207577397178
99 01 21 -0.566207577397178
99 01 24 -4.99197737117322
99 02 13 -1.15031932682955
99 02 18 -5.733349976222
99 02 23 -0.869496370371678
99 03 06 -0.319083375714252
99 03 19 -1.35251185547922
99 03 24 -1.33004601896259
99 04 11 -0.229220029647733
99 04 16 -0.521275904363918
99 04 22 -1.2626485094127
99 05 07 -0.453878394814029
99 05 10 -1.35251185547922
99 05 24 -1.97032235968653
99 05 30 -0.330316293972566
99 06 06 -1.24018267289607
99 06 23 -0.0157945827397513
99 06 27 -2.86895582035172
99 07 03 -1.04922306250472
99 07 08 -0.375247967005826
99 07 24 -0.139356683581214
99 07 28 -1.50977271109562
99 07 31 -0.465111313072344
99 08 20 -4.35170103044927
99 08 22 -4.86841527033175
99 08 25 -4.03717931921646
99 09 01 -2.2511453161444
99 09 05 -3.22840920461779
99 09 07 -2.98128500293486
99 09 09 -3.28457379590937
99 09 16 -4.08211099224972
99 09 18 -4.00348056444151
99 09 21 -4.17197433831624
99 09 25 -3.11608002203464
99 09 29 -3.85745262708342
99 10 03 -3.77882219927522

and my code is:
data <- read.table("AUTOFD2a", col.names = c("year", "month", "day","fd"))

new.century <- data$year < 50

data$year <- ifelse(new.century, data$year + 2000, data$year + 1900)

data$date <- as.Date(ISOdate(data$year, data$month, data$day))
x1 = data$date

 library(date)

c1a<-rgb(1,0,0,8/9)
hist(x1,breaks="years",freq=T,axes=F,col=c1a)


data <- read.table("MANFD2a", col.names = c("year", "month", "day","fd"))

new.century <- data$year < 50

data$year <- ifelse(new.century, data$year + 2000, data$year + 1900)

data$date <- as.Date(ISOdate(data$year, data$month, data$day))
x2 = data$date

c2a=rgb(0,0,1,8/9)
hist(x2,breaks="years",freq=T,axes=F,add=T,col=c2a)
 axis.Date(1, at=seq(as.Date(min(x1)), as.Date(max(x1)), by="years"))
 axis(2)
legend("topright", c("AUTO", "MANUAL"), col=c("red", "blue"), lwd=10)

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