Parking shown in tatty A to Z, rather yellow (5)
I believe the answer is:
topaz
'rather yellow' is the definition.
'topaz' can be an answer for 'yellow' (I have seen 'dark yellow' mean 'topaz' so perhaps 'yellow' could also mean 'topaz'). I am not certain of the 'rather' bit.
'parking shown in tatty a to z' is the wordplay.
'parking' becomes 'p' (abbreviation on road signs).
'shown in' is an insertion indicator.
'tatty' is an anagram indicator (I've seen this in other clues).
'a'+'to'='ato'
'ato' anagrammed gives 'toa'.
'p' placed within 'toa' is 'topa'.
'topa'+'z'='TOPAZ'
Can you help me to learn more?
(Other definitions for topaz that I've seen before include "Yellow quartz used for gemstones" , "Shade of yellow -- gem" , "Yellow or pale blue gem" , "valuable item" , "Silicate gemstone" .)