[BUG] SVG Export uses RGB colors in SCSS notation

[mosc9575]

Software versions

Python version : 3.12.4 (tags/v3.12.4:8e8a4ba, Jun 6 2024, 19:30:16) [MSC v.1940 64 bit (AMD64)]
IPython version : 8.25.0
Tornado version : 6.4.1
NumPy version : 1.26.4
Bokeh version : 3.6.1
BokehJS static path : ~/Envs/fbpinn/Lib/site-packages/bokeh/server/static)
node.js version : v20.17.0
npm version : 10.8.2
jupyter_bokeh version : 4.0.5
Operating system : Windows-10-10.0.19045-SP0

Expected behavior

I expect, that I can save a figure to a file as svg and when I open it another program, it is displayed correctly.

Observed behavior

When I save a plot as a figure using the latest version ob bokeh 3.6.1 and open this file in inkscape or in python using reportlab, colored areas are defected. The color is not evaluated correctly and mostly shown in black.

Please notice, that this defect is not visible, if I open the file in a modern browser. Then the newer version is displayed in the correct from.

Reading the source code of the older and the newer versions shows, that the values inside an rgb call is changed. The older was rgb(222,222,222) which looks like valid CSS, while the newer is rgb(222 222 222) which looks like SCSS/SASS.

3.4.3	3.6.1
<path fill="rgb(202,178,214)" stroke="rgb(202,178,214)">	<path fill="rgb(202 178 214)" stroke="rgb(202 178 214)">

Example code

import bokeh
from bokeh.io import export_svg
from bokeh.plotting import figure

v = bokeh.__version__

p = figure(title=f"SVG export in {v}", tools="")
p.rect(x=[1, 2, 3], y=[1, 2, 3], width=1, height=1, color="#CAB2D6")
p.output_backend = 'svg'
export_svg(p, filename=f"export_svg_{v}.svg")

Screenshots

[mattpap]

rgb(222 222 222) which looks like SCSS/SASS.

rgb(R G B) or rgb(R G B / A) is CSS 4 color syntax. I suppose SVG still supports officially only CSS 3 (or lower). If that's the case, and that needs to be confirmed with SVG specification, then we will have to make sure that all generated colors conform to the correct CSS level. Browsers may support newer levels of CSS where programs like Inkscape will not.

[mattpap]

From https://www.w3.org/TR/SVG2/painting.html#Definitions:

For any value, all color syntaxes defined in CSS Color Module Level 3 must be supported, including rgb(), rgba(), hsl(), hsla(), the extended color keywords and the currentColor value.