I don't understand why SVG symbols, which are colors changeable in the symbol default installation like this airplane:
whereas there symbols like the transport bus station, and lighting symbol (that i have been created in inkscape 0.91) that don't have any option to change the fill colors and the outline?
I have red Changing colours in SVG symbol using QGIS? and didn't got suitable answer.
You need to modify the content of the SVG file and an answer was given in GIS SE (How to create svg symbols that have modifiable fill color, stroke color and stroke width?) and in Add and personalise SVG symbols in QGIS (in French, Portail SIG)
Compare the "transport_bus_stop.svg" file where you can change the colors
In the file, the <path contains many parameters fill, fill_opacity, ...
<g><path fill="param(fill)" fill-opacity="param(fill-opacity)" stroke="param(outline)" stroke-opacity="param(outline-opacity)" stroke-width="param(outline-width)" d="M290.625,34.563c0.676,0,1.379,0.026,2.063,0.031
c0.688-0.005,1.381-0.031,2.063-0.031H290.625z"/>
And the "transport_bus_station.svg" file where you cannot change the colors, none of them.
<g><path d="M289.075,74.971c0.53,0,1.08,0.021,1.616,0.025c0.539-0.004,1.082-0.025,1.615-0.025H289.075z"/>
Therefore if you add these tags (fill=,...) after each "<path" and before d=" in the file:
<path fill="param(fill) #FFF" stroke="param(outline) #000" stroke-width="param(outline-width) 1"d="M289.075,74.971c0.53,0,1.08,0.021,1.616,0.025c0.539-0.004,1.082-0.025,1.615-0.025H289.075z"/>
The result is a symbol where you can change the color, the stroke and...
The new paths of the "transport_bus_station.svg" file
<g>
<path fill="param(fill) #FFF" stroke="param(outline) #000" stroke-width="param(outline-width) 1"d="M289.075,74.971c0.53,0,1.08,0.021,1.616,0.025c0.539-0.004,1.082-0.025,1.615-0.025H289.075z"/>
<path fill="param(fill) #FFF" stroke="param(outline) #000" stroke-width="param(outline-width) 1" d="M400.596,94.753c-21.278-8.867-72.277-19.462-109.904-19.758c-37.625,0.298-88.604,10.892-109.88,19.758
c-21.582,8.993-35.975,17.989-40.471,40.47l-16.183,124.644v171.725h27.886v26.933c0,32.837,48.036,32.837,48.036,0v-26.933h88.727
h0.27h92.228v26.933c0,32.837,48.062,32.837,48.062,0v-26.933h27.886V259.867l-16.183-124.644
C436.57,112.743,422.178,103.746,400.596,94.753z M222.187,106.456h66.888h70.144c13.489,0,13.489,20.223,0,20.223h-70.291h-66.741
C208.698,126.679,208.698,106.456,222.187,106.456z M176.085,377.754c-12.729,0-23.063-10.311-23.063-23.039
s10.333-23.063,23.063-23.063s23.039,10.332,23.039,23.063S188.815,377.754,176.085,377.754z M289.075,272.99H166.806
c-11.97,0-14.469-8.596-13.294-17.261l12.608-90.392c1.73-10.982,5.435-18.215,19.685-18.215h103.123h106.648
c14.25,0,17.979,7.233,19.709,18.215l12.608,90.392c1.176,8.665-1.349,17.261-13.318,17.261H289.075z M405.321,377.754
c-12.729,0-23.063-10.311-23.063-23.039s10.334-23.063,23.063-23.063c12.729,0,23.038,10.332,23.038,23.063
S418.05,377.754,405.321,377.754z"/>
<path fill="param(fill) #FFF" stroke="param(outline) #000" stroke-width="param(outline-width) 1" d="M492.577,87.888C438.591,33.902,366.813,4.17,290.466,4.17S142.34,33.901,88.354,87.888
C34.368,141.874,4.636,213.652,4.636,290c0,76.348,29.731,148.126,83.717,202.112c53.986,53.985,125.764,83.717,202.112,83.717
c76.349,0,148.125-29.731,202.111-83.717c53.985-53.986,83.717-125.765,83.717-202.112
C576.293,213.653,546.563,141.874,492.577,87.888z M290.466,550.692C146.72,550.692,29.774,433.746,29.774,290
S146.72,29.308,290.466,29.308c143.745,0,260.691,116.946,260.691,260.692S434.211,550.692,290.466,550.692z"/>
</g>
