pandoc: Undefined control sequence \colorbox - pdf

Question

Problem
I have a file with a combination of Markdown and LaTex that I would like to convert into PDF. Pandoc seems to work in Ubuntu 20.04 but not in Debian 10.
My Installation
# Installing Pandoc and dependencies
apt-get install pandoc texlive-xetex texlive-latex-recommended
My Markdown
I have the following text in a file called test.md:
\centerline{\Large{\textbf{Test 1}}}
\colorbox{blue!25}{\Large{\textbf{Test 2}}}
**This is a test**
Convertion
# Conversion
pandoc -V geometry:margin=0.7in -s test.md -o output.pdf
In Ubuntu 20.04 a beautiful PDF i generated.
In Debian 10 (Docker) I get the following error:
! Undefined control sequence.
l.62 \colorbox
Am I missing some dependencies in Debian 10? Is there a way to see what Pandoc engine that is used by default? What am I doing wrong?
When running verbose mode it seems the installations are using different engines, however, when I specify the geometry driver such that they are the same, the problem remains.
# Debian 10
*geometry* driver: auto-detecting
*geometry* detected driver: xetex
# Ubuntu 20.04
*geometry* driver: auto-detecting
*geometry* detected driver: pdftex
Update: Workaround
Reading several posts on similar problems, I first tried to add \usepackage{xcolor} to the start of the document, but that didn't work. Then I found out that you have to add a YAML-header and then it works. The original problem however still puzzles me.
# Adding this to the start of the document fixed the problem
---
header-includes:
- \usepackage{xcolor}
output:
pdf_document
---

Answer 1

Debian 10 (buster) ships with pandoc 2.2.1, while Ubuntu 20.04 (focal) comes with pandoc 2.5. It seems that you hit a bug which was fixed in the later version.
However, this is curious. The changelog mentions that a bug like this was fixed in version 2.6, which is newer than either of your versions. So I'm honestly a bit puzzled about the exact nature of the bug you triggered.