I have a problem with the coloured tables that I want to include in my master thesis, so it is a very important issue for me. I generate the tables with tablesgenerator.com, and in the LaTeX viewer they look amazing, but then in the PDF some lines just don't appear. If I zoom in the PDF, they appear again, but obviously anybody is going to read my TFM with a 200% of zoom. I have been reading some posts in this web and they say that it is because of the background color of the cells, that overlaps the lines, but I don't know how to fix it. I have read that some people use the command \setlength\arrayrulewidth{2pt}, and this solved my problem partially. The problem is that, obviously, I have to send my work to the teachers, and I don't know if they are going to be able to see the lines using this 2pt, or they would need more. That's why I think this is not a really good solution. I have read also that another people uses \tikz, but after having read many posts about it, I still don't know how I could implement this command specifically in my table, to draw the lines after the background.
This is my code:
\begin{table}[H]
%\setlength\arrayrulewidth{2pt}
\resizebox{\textwidth}{!}{%
\begin{tabular}{|l|c|c|c|}
\hline
\rowcolor[HTML]{C0C0C0}
\multicolumn{4}{|c|}{\cellcolor[HTML]{C0C0C0}\textbf{TFM TASKS}} \\ \hline
\rowcolor[HTML]{EFEFEF}
\textbf{Task} & \textbf{Description} & \textbf{Starting date} & \textbf{End date} \\ \hline
\rowcolor[HTML]{FFCCC9}
\cellcolor[HTML]{FD6864}\textbf{Project start} & \begin{tabular}[c]{@{}c@{}}First meeting at which the project was planned (its \\ structure and the objectives to be achieved at the \\ end of the project).\end{tabular} & 30/11/18 & 30/11/18 \\
\hline
\rowcolor[HTML]{FDF0AD}
\cellcolor[HTML]{F6DB53}\textbf{Theoretical analysis} & \begin{tabular}[c]{@{}c@{}}Initial study of the system based on the \\ documentation\end{tabular} & 01/12/18 & 23/12/18 \\ \hline
\rowcolor[HTML]{77CA5C}
\multicolumn{4}{|c|}{\cellcolor[HTML]{77CA5C}\textbf{Matlab simulations}} \\ \hline
\rowcolor[HTML]{CFEAC6}
\textbf{\begin{tabular}[c]{@{}l@{}}Development of \\ equations\end{tabular}} & \begin{tabular}[c]{@{}c@{}}The first equations were developed in Matlab, \\ verifying that the results from the University of \\ Rochester {[}REF{]} were obtained for the cases of 3 \\ and 4 lenses. Later, the system was generalized for \\ the case of 5 lenses, obtaining the first problems.\end{tabular} & 24/12/18 & 10/01/19 \\ \hline
\rowcolor[HTML]{CFEAC6}
\textbf{Meeting} & \begin{tabular}[c]{@{}c@{}}To comment on the progress made and try to solve \\ problems in simulations with Matlab.\end{tabular} & 31/01/19 & 31/01/19 \\ \hline
\rowcolor[HTML]{CFEAC6}
\textbf{Meeting} & \begin{tabular}[c]{@{}c@{}}To compare the Matlab equations and try to find \\ the solution.\end{tabular} & 06/03/19 & 06/03/19 \\ \hline
\rowcolor[HTML]{CFEAC6}
\textbf{Meeting} & \begin{tabular}[c]{@{}c@{}}Finally, we fixed the problem with the Matlab \\ equations.\end{tabular} & 08/04/19 & 08/04/19 \\ \hline
\rowcolor[HTML]{CDA7F6}
\multicolumn{4}{|c|}{\cellcolor[HTML]{CDA7F6}\textbf{Zemax simulations}} \\ \hline
\rowcolor[HTML]{F2E7FD}
\textbf{Zemax Installation} & \begin{tabular}[c]{@{}c@{}}We had some problems during the installation of the \\ program due to the Windows version of the computer.\end{tabular} & 01/01/19 & 03/03/19 \\ \hline
\rowcolor[HTML]{F2E7FD}
\textbf{First steps with Zemax} & First days learning to use the program. & 25/03/19 & 30/03/19 \\ \hline
\rowcolor[HTML]{F2E7FD}
\textbf{Meeting} & \begin{tabular}[c]{@{}c@{}}Skype meeting to clarify some doubts regarding \\ Zemax simulations.\end{tabular} & 27/04/19 & 27/04/19 \\ \hline
\end{tabular}%
}
\end{table}
With this, in LaTeX, I obtain:
Nevertheless, in the PDF I obtain:

It is very important that all lines appear in the Tables, because I have several ones that can't be understood if this happens. Therefore, I would greatly appreciate your help. Thank you.




